That creates a precedent and every “dangerous ideology” will then be deplatformed and censored.

Considering how actual anticapitalist people get subjected to state oppression, I tentatively agree, but I also think, that, considering how actual anticapitalists are subjected to state oppression (see Chiles socialist government being infiltrated by the CIA, and the CIA having official documents saying that they did in fact do vote manipulation), we live in a world where this is already kind of true.
Every ideology that is specifically dangerous to the powers and laws that be, is allowed less power, than ideologies that aren't

Hatred is not defeated with censorship and violence.

The nazi kind definitely is, maybe not fully, but a significant part is. Again, see WWII and the aftermath, especially in Germany.
Also see this interview with Vaush (watch from the timestamp until 12:45, should be enough)

There is a black man who becriended countless KKK members who even left the group because that black man showed them love, understanding and made them question everything they believed in.

A worthy endeavor, but both can be done, the world is multi-threaded. This kind of conversion by love works best when people are on the fence.