Thank you for explaining. I find the media often quite misleading. The media here had stated that while NL of course was within their rights to deny Turkish campaigners entry into NL, to apprehend a foreign person who was legally in the country on her way to her embassy/consulate without any sort of warrant was extremely controversial.
Then again Germany is very big into Assumption of Innocence: a couple of months ago, an armed man appeared on the roofs of some buildings opposite the administration of this province, the police did show up, however, since the man wasn't shooting anybody (yet?), they had to leave him there...until he was actually doing something illegal, the threat alone isn't enough.
Anyway: I think the biggest issue with the Erdogan dilemma is the dual citizenship. Technically you have to give up any other nationality when you apply for a German citizenship, or you have to give up your German passport if you apply for citizenship of any other country. The only exemptions are when you were born with two nationalities. (either because you receive German citizenship thru birth in Germany, while also eligible for another nationality due to your parent's citizenship, or vice versa)
Many German-Turkish people in Germany for ex, were granted the citizenship on the condition that they had to give up their former Turkish ones, which they did for about 15 min, then after the German passport was issued, the Turkish embassies re-issued their Turkish passports again. Illegal, but German simply turned a blind eye.
Now Germany is home to a lot of people who can vote both in German as well as in Turkish elections - thus making Germany a very important campaign area. I was not aware that NL was in an equal position. BTW, a lot of US presidential candidates also come overseas for campaigning. They however speak to the US armed forces on Us military grounds.
According to the Dutch language Wiki about double nationality:
"..Op 1 januari 2011 woonden er in Nederland 1,2 miljoen personen met zowel de Nederlandse als ten minste ??n andere nationaliteit. Bijna de helft van deze gevallen betreft het mensen met naast de Nederlandse ook de Turkse of Marokkaanse nationaliteit. Het aantal mensen met een dubbele nationaliteit is in tien jaar tijd bijna verdubbeld. De stijging van het aantal Nederlanders met meer dan ??n nationaliteit kwam tot 2003 vooral door naturalisaties. Bij hun naturalisatie krijgen mensen de Nederlandse nationaliteit maar ze kiezen er meestal voor om ook hun oorspronkelijke nationaliteit te behouden. Wettelijk gezien mogen mensen die kiezen voor naturalisatie sinds 1 oktober 1997 hun oude nationaliteit niet meer behouden. Vanaf die datum geldt in Nederland de hoofdregel dat iemand, die door naturalisatie Nederlander wordt, zijn oude nationaliteit moet opgeven "tenzij dat in redelijkheid niet van hem kan worden gevergd" . Er zijn daarnaast nog een aantal uitzonderingen. Dit moet de genaturaliseerde persoon zelf regelen. Als men binnen drie maanden na de naturalisatie geen verzoek indient tot afstand van zijn oorspronkelijke nationaliteit bij de IND en bij de autoriteiten van het land van herkomst, dan kan zijn Nederlandse nationaliteit weer worden ingetrokken. Er zijn heel veel uitzonderingen op de hoofdregel, waardoor bijna 80 procent van de genaturaliseerden na 1 oktober 1997 toch de oorspronkelijke nationaliteit kon behouden naast de Nederlandse. Sinds 2003 neemt het aantal Nederlanders met een dubbele nationaliteit vooral toe door geboorte. In 2007 waren er 21.000 kinderen die bij de geboorte automatisch een dubbele nationaliteit kregen, omdat ??n van de ouders naast de Nederlandse ook een niet-Nederlandse nationaliteit had. Na naturalisatie verliest een genaturaliseerde persoon soms automatisch zijn oorspronkelijke nationaliteit. Dit geldt bijvoorbeeld voor mensen uit China (behalve Hongkong en Macau), Suriname en veel landen in Afrika. Vaak is dat echter niet het geval en moet de genaturaliseerde persoon officieel afstand doen van de oorspronkelijke nationaliteit. Het is echter niet altijd mogelijk om na naturalisatie afstand te doen van de oorspronkelijke nationaliteit, omdat niet alle landen dat toestaan. De IND meldt dat er ? voor zover bekend ? ongeveer twintig landen zijn die niet toestaan afstand te doen van de nationaliteit van dat land, waaronder Griekenland, Marokko, Mexico en Iran.[8 ]..."
"...On January 1, 2011 there were 1.2 million people in the Netherlands with the Dutch and at least one other nationality. Nearly half of these cases these people had in addition to Dutch, the Turkish or Moroccan nationality.  the number of people with dual nationality has almost doubled in ten years. the increase in the number of Dutch people with more than one nationality was until 2003 mainly by naturalization. In their naturalization people obtain the Dutch nationality, but they usually choose to alsoretain their original nationality. Since October 1, 1997 it is not allowed legally for people who opt for neutralization to maintain their old nationality. The main rule is that a person who is a naturalized Dutch citizen from that date must give up his/her old nationality, "except if it can not reasonably be expected of him/her" . Besides that there some other excemptions. The neutralized person has to arrange it for themselves. If one does not submit a request to renounce his/her original nationality at the IND and the authorities of the country of origin within 3 months of neutralization, his/her Dutch nationality may be revoked. There are many exceptions to the general rule, which still almost 80 percent of naturalized after October 1, 1997 could retain their original nationality alongside the Dutch. Since 2003, the number of Dutch with dual nationality mainly increases by birth. In 2007 there were 21,000 children who received dual citizenship automatically at birth, because one of the parents had in addition to Dutch non-Dutch nationality. Sometimes after naturalization the naturalized person loses his/her original nationality automatically. This applies to people from China (except Hong Kong and Macau), Suriname and many countries in Africa. Often that is not the case and the naturalized person must formally renounce their original nationality. However, it is not always possible to do away after naturalization of the original nationality, because not all countries allow it. The IND reports that - if known -. About twenty  countries that do not allow to renounce the nationality of that country, including Greece, Morocco, Mexico and Iran [8 ] ... "
The latest official figures with regard to dual nationality from the Central Bureau for Statistics (CBS) date from 2014, when 1.3 million Dutch had two passports. Turks and Moroccans were the largest groups of respectively 312 thousand and 311 thousand with dual nationality.
Children of Turkish and Moroccan parents are automatically Turkish or Moroccan. Even if the child is not declared to the civil registry in the country of origin.
Apparently since 2014 it is no longer kept up if someone has a another/dual nationality.
There are countries where you can not give up your nationality, such as Morocco. The country provides no possibilities to give up the Moroccan nationality. Morocco is it not unique. Even Queen M?xima can not get away from her Argentine passport. The same applies, for example, Greeks and Iranians and about twenty other nationalities.
Children of Turkish parents automatically receive Turkish citizenship. But other than Dutch Moroccans they do have the possibility to waive later. Anyone who wants to give up their Turkish nationality has to submit a request at the consulate. Within a month of three this would then have to be settled.
For men it is moreover a little more complicated than it seems at first glance. All Turkish men till 45 years should perform their (Turkish) military service. For Turks older than 38 years this is something they have to do first. They can also redeem military service for about 1000 euro. For young Dutch Turks, this is now no longer. But according Adalet, a consultancy for Turkish law, there are some other conditions. Who wants to give up Turkish nationality, must not be engaged for example in a criminal case. The past year there was the issue with a Dutch-Turkish (female) journalist Ebru Umar. She was among others accused of insulting Erdogan by Twitter and received house arrest when visiting Turkey. Because of all this Ebru, who kept her Turkish nationality to please her parents, wanting to give up Turkish nationality. As she was in a criminal case (insulting of Erdogan among others) she could not give it up (yet). https://en.wikipedia.org/wiki/Ebru_Umar