Scared of what?
I can't speak for conservatives, nor republicans, but from a more libertarian point of view, I have no problem with Mamdani.
Because once he destroys NYC, and the rest of us (aka capitalists) have to bail it out, we'll be good for another 20 years or so until there's a fresh crop of young people who have no clue that communism and socialism always fail, so they'll want to try it again.
In other words, cheesy, once the so called 'billionaire' or 'millionaire' class moves out of NYC, and the communists have no one left to tax, the whole thing falls apart.
Now that he's going to be in command, just watch what this guy does. Two main things will happen. More govt programs = more control over individuals' lives, and he will (I think he has already started) crack down on free speech.
Communism and free speech are 100% incompatible. That's why the 1A is so important.