>"nobody is illegal"

This is completely orthogonal to the conversation, but I think you misunderstood that slogan. It does not mean “immigration rules must not be enforced”.

It means differentiating between a potentially illegal action (illegal entry/overstaying) and the person itself. You never talk about an illegal driver, or an illegal drinker, but people talk about illegal immigrants, with the implication that the person itself is illegal.

It’s subtle but it’s a step towards dehumanizing a person, or making infractions to their rights “count less” in the public eye.

> but people talk about illegal immigrants

Worse than that, we more and more often just see the term "illegals" being used, which completely removes the person from the description.