And yet multiple studies have shown that when jobs are offered to Americans that involve labor (farm, construction, food industry), at those wages, then there are generally few to near zero applicants.
There are other reasonings (prevailing wage, location, etc.), but likewise, your "absolute assertion" that undocumented workers have been taking job opportunities from you is also not entirely ... absolute.
The key point is "at those wages". The overall assumption in the economy is that it's good and proper for low-skilled jobs to be very low paying, despite otherwise being very unattractive. As long as people are unwilling to pay the proper cost for hard labor, they'll keep hitting this problem of local people not willing to do the work for a pittance. Then, when they circumvent the local workers, they'll be surprised that local workers are discontent.
I do agree with that. The same as with the trope about McDonalds, etc. being "starter jobs" for teenagers, etc., and that's why it's okay for them to not pay a liveable wage, etc., which has no origin in fact (re the minimum wage law) and only in Republican ideology.
There are other reasonings (prevailing wage, location, etc.), but likewise, your "absolute assertion" that undocumented workers have been taking job opportunities from you is also not entirely ... absolute.