Just now got to see your reply and thanks for that.
IMO, the problem is that new jobs will not be created in order to meet the supply of new workers.
Using the understated government figures from this year, 11.7 million are currently out of work. By adding another 15 million to the work force, where will available jobs come from? Even if those working here “under the table” now go on the tax roles, a likely consequence will be employers actually reducing the number of available jobs, as putting these jobs “on the books” will be expensive for employers.
What I strongly suspect is that a huge of number of this new work force will, as you stated, see a bigger benefit in receiving government assistance versus working for a pay cut, as this new work force isn’t stupid either.
In many cities, the minority community and other lower-income populations have still not seen much improvement in employment. These vulnerable neighborhoods with cheap housing is where this new wave of hispanics will live. There could be a really awful clash of cultures, with demand greater than supply for jobs, services, police protection, dominance etc. It wouldn't take much to have all-out inner city chaos.
Inner cities need entry level and lower wage jobs. They need them for US citizens. Thinking that this situation can be remediated while tens of millions of people with a different culture and no desire to assimilate are made legal is insanity.