Well most countries handle it this way. You get your visa revoked and thats it. Pretty normal stuff and rarely is a judge involved. In the usa they dont even need to revoke a visa to throw you into guantanamo it seems. Non citizens normally dont have a right to stay in a country. It is a priviledge not a right.

I am not sure how i feel about needing a lot of evidence to rewoke visas.

In this case 3 ppl are eu citizens and the eu "freizügigkeit" needs more evidence than just allegations. However when a few neo nazi hooligans from ireland would storm into a university i would like them to be deported, especially if they dont even say the allegations are wrong. So i have to admit i am indifferent in this case.

Under german law it is enough of a reason to get deported when the german immigratsoffice things that you are a threat to public safety. They dont need legal proof. having a lawsuit against you of a serious crime is enough for that. Eu law says that you need more reason to be deported, but that is eu law not german law.

Thats why the american gets deported and doesnt file a lawsuit, while the 3 europeans did (and most likly can stay in germany till their lawsuit for destroying university property of at least 100k, attack with hatches, bats and heavy equippment, defamation and usage of unconstitutianal symbols and parols comes to a conclusion)

I am not here is an article for you so you can read up on it https://www.welt.de/politik/deutschland/article255845278/Wegen-Stuermung-von-Uni-Gebaeude-Erstmals-Exempel-statuiert-Berlin-plant-Ausweisung-auslaendischer-Israel-Hasser.html

While it is true that they are not convicted, all 4 of them are prime suspects in the destruction of university property and in threatening university staff with weapons, which is legally enough of a reason to throw even eu citizens out.