I don't think this is quite true. People that call themselves centrists can come from a benign place. In my mind, the folks that call themselves centrists tend to mainly care about preserving the status quo, no matter what it is.

They'll usually use terms like "big tent", "adult in the room", and if they went to school "realpolitik". Usually privileged, they don't understand the urgency for change for those in need, so they'll balk at any method that may actually achieve some progress for the marginalized and underprivileged. Usually they'll say some wise, enlightened thing about "optics".

And they'll tell themselves that they care. They'll tell themselves and others that they're the good guys. They'll watch CNN and read the economist, and they'll tell themselves they're informed. They're always on the right side of history, but only ever when it's already too late. I think they genuinely don't know.

You're both right and wrong.

“Centrist” is just what conservatives, corporatist parasites, and / or fascists call themselve

This is true.

There’s no such thing as a centrist.

This isn't. There absolutely are centrists, it's just that their voices are drowned out by the loud extremes, AND they're being labelled as leftists by the right, and "rightists" by the left.