Leaving religion aside, it would be insane to allow  the ministers of Turkey to solicit votes from expats in their adopted country to support a dictator back home.
1. The Netherlands is not a province of Turkey.  Erdogan has no respect for the sovereignty of a foreign country.
2. One questions the loyalty of these expats if they still feel such a strong attachment to Turkey.
3. If the Dutch didn't shut this down the govt would be accused of tolerating a fifth column. 
4. This spectacle does not help the pro-immigration argument in Europe when there is already much populist sentiment against outsiders.