I have never heard of people being "penalized". If you violate the law, for example by discriminating someone, you can get a penalty indeed.
You can have all your "anti-immigration sentiments", but you are not going to be penalized. You can be completely opposed against immigration, and if you have some good arguments, you can calmly post them anywhere. I fear that "sentiment" is doing a lot of work here.
Besides: what looks like organic in extremist circles is often not. You start with a business model and you will gather a herd. You just have to feed them.
European countries are under attack by the Russian regime, if you missed it. Immigration was and is used as a weapon to destabilize European countries. Russia was/is financing immigration hostile parties and organizations in Europe.