They are disobeying a law that is not being enforced. If you lived in abject poverty in Mexico and your only hope of economic survival for you and your family was to cross over an unguarded border and break a law in another country which is not being enforced, would you not move heaven and earth to do it?
I don't have anywhere near as much animosity for the illegal aliens as I do for the politicians and employers who encouraged them to come here and break our laws.
Your position is one I have seen liberals take many times. It's why those laws may never get enforced. You're on the wrong side.