Why do they think it will stop at a few million?
If we signal that we're not going to enforce our laws due to the cruel actions of the parents, why would any parent not sneak their kids in, foo? The argument will be the same in 5, 10, 20 or 50 years.
I'm sure some would argue that we're going to put more laws on the books that will prevent this in the future. I'd mention we had laws on the books already, and those were broken. If we can ignore them now, won't we ignore the new ones too? Did I mention the argument will be the same?