as mentioned, in the long-run, i would support essentially erasing the borders of the nafta states to start, and then gradually erasing more and more borders as the class relationships absolve.
but, i do see the world in terms of class, and i know which class i stand with. so long as the rules in this country are erected so that migrant labour benefits the middle class at the expense of the working class in a way that is strictly exploitative, the state should be implementing rules to prevent that exploitation from occurring - which means criminalizing illegal border crossings, however nominally.
there should also be a strict crackdown on people that "sponsor" these refugees in order to exploit them. let's drop the bullshit - these people are buying and importing slaves. that should be ended immediately, and they should face steep punishments for it. it's the unscrupulous employers that really deserve stiff and lengthy jail sentences, not the imported workers.
the point is to incentivize proper entry procedures, and if the policy is successful then it will lead to lower crossings, not more people in jail.
but, there is nothing left-wing about supporting systems that exploit migrant labour - that is support for modern day slavery.
if you can't work that out, or you're too selfish to care, you should be ashamed of yourself.