The ACLU gets involved in those cases because majority thinking sometimes tramples on the rights on the minority, and somebody needs to point out the legal principles that protect that minority. That's the reson, by the way, we live in a republic, not a democracy. The founding fathers felt that if we had a democracy, we would be subject to the tyranny of majority rule. Instead, with a Republic, the majority would elect lawmakers who would, in turn, excercise their political skills to chart a course that would be right for the country, even if the majority were howling about something else. The founding fathers didn't trust the general public to get it right, for they knew how mob rule works.
Similarly, the ACLU doesn't just 'go along' with what 'everybody wants' because sometimes 'everybody' is wrong. If there are legal issues that are being overlooked by the majority, it is their duty to stand up and say so, no matter how unpopular this makes them. Sometimes I agree with the ACLU, and sometimes I think they are idiots. But I greatly appreciate the role they play, for they are consistently on the side of law, and society needs a gadfly to be like that. Look at the current political climate, and how willing most Americans are to throw away their constitutional rights over an emotional decision. If politicians came out with the America First! Bill, and said it would 'fight terrorism' by requiring all those with Arabic names to register with the police and be under constant surveillance, there would probably be a large number of Americans who would applaud this move. The fact that it would be totally unconstitutional wouldn't even occur to them, let alone matter. But the ACLU would step in immediately, as well someone should, so that the next time it won't be all those with Irish names, or Italian, or as with World War II Japanese names. If you don't step in when the thin edge of the wedge is being applied, you run the risk of being too late to stop the whole door from being broken in.
So even if you hate the specific acts the ACLU takes, you should appreciate the principle of what they are doing. Maybe they aren't protecting your rights this time, but if they didn't protect the rights of those you despise, next time it could actually be you that becomes the target.