Lots of people immigrate illegally, and many of them stay at length, work hard, and build lives. The government pretty explicitly turns a blind eye to their presence. Then we change leaders, and suddenly responsible residents of 30 years are kicked out to a country they haven't lived in since childhood. Meanwhile, a great many other people in the same situation aren't.
It's a bit like my reaction to marijuana laws. I think the law isn't very good, but that's just grounds for reform. What I think is immoral is seriously punishing 1% of people violating an unimportant law instead of lightly punishing lots of them. It's about limited or variable enforcement of the law, which encourages people to play a lottery where a handful of players get their lives ruined.