Why does the "left" portray themselves as morally superior much more often than the "right"?

What's even funnier is that the unjustified "moral superiority" stems from self-righteousness. Whenever a "centrist" disagrees with their position, the centrist is automatically labelled a right-winger at best and a Nazi at worst. To be fair, the same behavior is seen in the "rights" against the "centrists" as well, but it's more seldom, IMO.

E.g. A "centrist" says they want the illegal immigrants to be deported. The "left" would say it's a racist statement by a Nazi, while all the centrist demanded the laws are enforced.

So, why are the left like that in a larger degree than the right? Is my view biased?

I am trying to put "left"/"centrist"/"right" in quotes as these labels are extremely imprecise and can be as useful as harmful.

UPD: please remove my post if it violates the community rules.