Why are ICE so strongly protested against/disliked?

This is not an agenda post. I’m pretty left wing and have my own views regarding immigration in my own country.

My question is more a case of trying to understand why ICE appears to be so strongly opposed.

As a general rule are people not happy to illegal migration being tackled? Is the issue that they’re not only targeting illegal immigration?

I know it’s a hot topic because of a shooting but aside from that it appears to have been pretty much the same before.