Laws exist to serve people, not the other way around.
Illegal immigrants often do not enjoy all the rights and privileges citizens of the United States do. Many underpaid, overworked, and denied benefits.
If we need more people in this country, we need to make it easy for them to come, and we need to treat them right when they arrive.
And I don't think open borders are a good idea for america in its current state.
SF doesn't keep illegal immigrants safe from deportation. It says "in these circumstances, we think it's more important that you cooperate with the city than it is for us to try to deport you, so we're going to call a temporary truce".
We all unwittingly break many laws day. Living in the US is inherently illegal, even if you happen to be a citizen. My point is that there isn't some binary division between people that break the law and those that don't.
If businesses need to be immigration police, they'll just hire illegal immigrants under the table (moreso), and be more exploitive about it.
If people are afraid to talk to the police, they won't. This breeds gangs & protection rackets, which presumably you don't want, because they increase crime.
As these problems will become worse and worse, the more we will try to crack down on illegal immigration, intensifying said problems. The tragic irony is that the solution is the cause of the problem and it is part of a nasty feedback loop.
I am guessing you are implying that the White Europeans "stole" America from the Native Americans. By that notion, you can keep going a few 100 years back in history and you'll eventually end up with "Living in the ___ is inherently illegal, even if you happen to be a citizen" for every place in this earth except that place in Africa where the human is supposed to have evolved and migrated.