This is the same grouping fallacy as the vaccine arguments. A lot of these people have trouble understanding nuance. The vaccine can be harmful to some and beneficial to others, it’s on a scale and it’s impossible to know who falls where on the scale. That doesn’t mean overall it’s a bad thing to do.

For op’s example there are some leftists who are lazy and weak, there are also some who are ruthless and there are some that are ruling class elites. The problem is when their groups are applied to the whole to suit whatever narrative they want it becomes nonsensical and dangerous.