
It is the companies who break the law and hire these undocumented workers - almost always at below minimum (or market) wage rates and with no benefits etc. - that deserve our ire. These companies are looking to maximize profits by exploiting these workers. They know they can't do it to Americans, so they create incentives for folks to risk their lives to come over for the work.
If companies weren't so greedy as to create the economic incentives to attract undocumented workers - then clearly there would be no immigration issue.