I am all for caring for immigrants, legal and illegal. Jesus' command is clear and if believers do not obey it, we are worse than unbelievers. (As an aside -- there's a whole understanding of the parable of the last judgment that has been lost on many people -- the parable is speaking about non-believers, not believers. "The least of my brethren," which most people understand to be humanity in general (and that's a perfectly valid understanding) is actually a term for believers. So the things Jesus lists for how people should treat others are the bare minimum for Christians to do. If we aren't doing those things, then we have no right in claiming the title of Christian.)
And the point the bishops are raising is perfectly valid and the article link above which extols them for doing so is correct. However, this is actually a fairly easy thing to do. Immigrants are people outside the womb. The mainstream press are all in support of what these bishops are saying. So when Cardinal Mahoney says he will tell his priests to disobey any law that would require them to ignore the needs of some who is not in our country, the MSM love it.
But should any bishop rebuke a politician for supporting abortion or embryonic stem cell research, then that bishop has stepped over the line. So it is much more difficult for a bishop to say anything about sexual and reproductive matters than it is on immigration matters.
Contrary to Bill O'Reilly, et al., the Church is not for the illegal immigrant because of declining membership. On the contrary, we're gaining members and can't keep up with them with the shortage of priests. Actually, it is more likely that the mainstream media want the illegals here because the general population is not reproducing itself. Without immigration, our population growth would be in the negative. Without immigration, the Democratic party and its MSM cronies would find itself facing what is called the Roe effect -- the fact that "liberals" are not so liberal-minded when it comes to reproducing themselves and are contracepting and aborting themselves out of existence. Without an influx of immigrants, who generally vote Democratic, there would be no future for that party. And without people, life's a pretty dull party.