Because you are encroaching on government's rule to protect you.
We now are living with federal supremacists. Kind of like those guys in the hoods or the white power bandits or the black power panderers except their extremism based on a combination of theft and enslavement.
Under the banner of freedom, we're witnessing the erosion of sovereignty. With the Supreme Court's decision which ultimately places federal jurisdiction over... well, everything... there are no longer states, or international borders for our home of the brave. That's right, the melting pot has reached a boiling point where the pot itself has liquefied and the whole mess is falling into the fire.
So if you're Arizona and you spot a thug up to no good in your neck of the woods, be sure not to chase him down and demand to know why he's there...that's the police's job...and if you stand your ground, even when the cops fail to come, you're in the wrong.
I fully anticipate that Arizona and all her sisters will develop some improved residency requirements...and if your credentials don't get you in the gated community, you'll be escorted off the property...to a state of sanctuary.
It seems to me that those in the federal pantheon seem to forget that it is from the states they derive their authority...and the relationship has gone from uncooperative to antagonistic. By undermining the very foundation of federalism, SCOTUS has invited termites into the foundation.
Unchecked illegal immigration is as destructive as any natural disaster, but a hurricane doesn't vote.
Will state troopers no longer be able to give tickets to speeders on interstate highways?
Will state taxes go away because federal tax supersedes the states' ability to tax?
Will town councils be superseded by the county in which they reside?
Until we return to individual responsibility, sovereignty will continue to disappear. It won't be long before you cannot have a firearm to protect your home...your castle...because you see it's someone else's responsibility and you're just going to have to wait for the government to decide when it will respond to your needs. You must wait your turn. You must eat your peas. You must endure the break-in. You must ignore the creepy van.