Oh yeah, it's the old "I've got mine now I don't want anyone else getting theirs." selfishness.
Doesn't impress me.
As far as other semiskilled laborers, they benefit from the increased economic activity resulting from a plentiful labor pool.
A good citizen employee is worth far more to an employer than a good illegal one. But a bad employee is worthless to all employers, and too many bad employees use Mexicans as a scapegoat for their own inability to keep a job.