While many have been condemning both the immigrants and their reasons ("under the table" foremen and farmers), their reasons for and means of immigration must be put into context.
Opponents of amnesty and supporters of a U.S./Mexico wall frequently cite the large influx of immigrants during the 19th Century through Ellis Island, pointing out their naturalization and dedication to this country's ideals and beliefs. While the former is true, the latter is merely assumed. In addition, those immigrants came from overseas which means places such as Ellis Island were their only way in and thus they had to enter legally.
To our South, however, is a vast border with jobs and families waiting for needy workers. Unlike Irish, German and Italian immigrants often cited, these needy individuals have a choice and the less time they waste, the sooner they can improve the lives of their families back home. And when their employers in the States care not that they speak English nor that they carry papers, what, honestly, is their motivation? Altruism? One could hope for that but when de facto segregation and prejudice still exist, few care enough to take that extra step.