I usually do not answer questions with the language ''pro illegal'' and much less a question asking why anyone would ''support illegal immigration.'' Since you had the common sense to include the word ''amnesty,'' I will add to "elpibe's" answer.
First of all, anyone in their right mind would never, and read it here, NEVER support ILLEGAL IMMIGRATION!!
To answer your question about why people have failed to present any facts that make sense to you, let me say that the level of political knowledge in this forum is RTR (reduced to the ridiculous) in almost all instances.
For example, just the way in which the questions are asked speaks to ignorance. The answers are no better because this forum suffers from ignorance in governmental, congressional issues. Anyone referring to people here as pro-criminals automatically sets up the arbitrary answer of nonsense. If you wish a real answer, ask it in the proper category of government; you have more sophisticated participants there. Otherwise, consider the semantics of how you pose your question regarding those for amnesty of the illegals residing in the USA. You will engage a different type of participant.
You state it's an easy question, but not when when you use the improper approach in making your inquiry. No one supports the "illegal immigration movement." People support or do not support the MANNER in which our government should deal with the cause and effect of our own government's lack of concern for the issue.
Therein lies the complexities of the REALITY (critical mass). So, for people who support complete security of BOTH borders, amnesty for the ones already here, and most assuredly a proper treatment of the human beings in question, we look beyond the personal agendas involved in the participants answering here.
If it were as simple as deporting them all, it would have already happened. If it were as simple as you make it, would Congress still be screwing around with it? To imagine that this monster problem can be resolved with the endorsement of people on the yahoo immigration category is ludicrous! To realize that the complexities of the cost involved in mass deportations brings another type of fallout is therein the CATCH22! So, doesn't it stand to reason, that Congress will work toward the lesser of the two evils? It should result in a win-win and you will never see a total mass deportation, because it is simply not rationally cost effective.