In most cases the illegal immigrants who are deported have committed some actual crime. When an employer is busted, usually the workers are not deported. The employer loses his trained staff, and they go work for someone else. At least this is what has tended to happen in El Paso, with which I am most familiar. So for Obama to say he won't enforce deportation is to say that he won't do anything different than is already done. There are not enough resources to deport all the undocumented immigrants who show up on the radar, and the damage to the economy that would result from their deportation would cause an outcry and backlash against that enforcement.
The issue of illegal immigration is explained in "The Road to Serfdom" in the chapter "Why the worst get on top."
"It seems to be almost a law of human nature that it is easier for people to agree on a negative program - on the hatred of an enemy, on the envy of those better off - than on any positive task. The contrast between the 'we' and the 'they,' the common fight against those outside the group, seems to be an essential ingredient in any creed which will solidly knit together a group for common action." - F.A. Hayek
In this case the common action is the election of "conservative" politicians. The left has their own convenient group of hated people - the rich.
The idea that immigrants take away jobs, that they use more welfare than citizens, or that they cause crime or won't learn the language are myths that are easily dispelled by sound economic analysis or factual data. But enough votes to win an election aren't going to come from the relatively small number of people who are able to understand economics or who are able to discern truth from data. Those votes are going to come from ignorant, dissatisfied people who settle for a convenient scapegoat for the ills that plague our economy.