We have to vote for a person, not specific positions. While I generally agree with him on visa workers, there are many other things I don't. And he says really obnoxious things.
Also, it's not about "those leftists". Conservatives and GOP have been happy to give businesses what they want to make a profit, including exploitable and cheap visa workers, and in many cases "illegals".
Lefties have been somewhat more likely to complain about visa worker issues than righties over the years in my observation. Overall, Trump is a generally centrist, by the way.