In Canada if you are here on a work visa you are building up Canadian experience which you can eventually translate into an application for permanent residence followed by citizenship. There is a clear path to follow for those who wish to do that. Moreover, even for those who don't, as legal workers here on a visa all the ordinary protections of our laws are in effect. While there are clearly some abuses and some problems I believe it's the clear goal of our government to create a process that is fair and humane.
In the US these workers are illegal, and so denied all the support and protection of the state that everyone else enjoys. They really are second class.
With this group now representing one person in twenty five it's ridiculous to claim it's just a few isolated people who broke the law. The US economy is building up a large class of laborers who exist outside the protection of labor law, paid less than legal minimums, denied access to police or health services, forced to work in unsafe conditions, and without recourse from abuse.
To argue that they are not part of the United States is ludicrous, they are as integral to the US economy as slaves once were.
Either put then on a clear path to citizenship, with access to the law and other services, or else implement reforms to eliminate them.
Continuing to build up an increasing labor force that is treated as if sub human, with tacit support by the government, really is not that far from slavery in the continuum of immoral behavior.