So who are the police supposed to arrest?

It's also illegal to help them in some states.

Legally spoken it's not a right statement. The "owner" is fined when he leaves his dog, which is his responsibility, out in the cold. You probably will get arrested even faster when you leave your child outside in the cold too.
But actually, churches should be fined when they leave people outside in the cold without helping them, because they claim responsibility for the wellbeing of people.

Not only perfectly legal but perfectly acceptable.