Another misleading comprehensive immigration reform talking point is that illegal aliens need to "get to the back of the line for citizenship". Many politicians and groups have said something similar; that specific quote is from an Obama editorial. And, it's highly misleading since there's really no such thing as the "back of the line": people are constantly joining the line and those currently in the line might have been there for over a decade. The only way there could be an actual "back" to the line is if we stopped legal immigration; there's very little chance of that happening.
The "line" is actually more like a toll road, with cars stretching back miles bunching up at toll booths. If, say, thousands of people left an event and got on the toll road, all those people would have an impact on everyone else on the road.
Likewise, amnestying millions of people would affect everyone else in line and all those who joined the line for years to come. If FBI-level background checks were done, at the current rate it would take five years to check 10 million people, assuming that we completely stopped doing those same checks on legal immigrants. And, obviously, that would have a very delitirious impact on those who followed our rules, delaying their applications by five years or more. If we divided our processing between illegal aliens and legal immigrants, it would take a decade to do the checks on 10 million illegal aliens. See also this.
One alternative is to increase the number of FBI agents, just so we can give amnesty. That would take a while, even assuming there are enough eligible applicants. Another alternative is to not do FBI-level background checks, something that would allow untold thousands of criminals to be legalized and would no doubt give citizenship to terrorists.