A fairly minor but prevalent one is speed limit laws. I personally feel most speed limit laws in North America are ridiculous. In almost every situation it is safe to drive significantly faster than the posted speed, so it seems fairly obvious that there's something wrong with the law itself.
Now, in this particular group I expect that isn't terribly controversial. But it can be a very unpopular opinion in some circles for two different reasons.
1) It's the law. You want to break the law?
And the somewhat more reasonable one:
2) Nothing is more important than human life. If driving slowly can save even one life, it's worth it. By advocating an increase to speed limits, you're valuing a few minutes of your time over people's lives.
Now, for one thing, it has been demonstrated by numerous studies that increased speed limits do not necessarily result in increased accident rates (in fact, often the opposite). But even leaving that aside. Say that an across the board increase to speed limits of X%^ results in a Y% increase in fatal crashes. For some sufficiently (very) small Y/X, would that not be worthwhile? It's callous, but it seems to me that it must be true. (I mean, look at the extreme case. Driving at any speed is much more dangerous than walking, but we do it anyway since it gets us places faster.) I definitely wouldn't feel comfortable saying so in a lot of peer groups though, nor without all the preamble.
^Not that that would be the most logical way to do it of course.
Edit: I should clarify that I'm speaking of main arterial roads and highways here, not residential streets. At least in most of Canada, almost all non-highways have speed limits of 50km/h, regardless of whether they're a residential side-street or a major 4 or 6 lane road. Most highways have limits of 80km/h, a few 100, and the highest I've ever seen is 110. In good conditions, most highways could easily be safely traveled at at least 120km/h. I don't think it makes sense to set speed limits for the worst case scenario, and ignore all the efficiency that could be safely gained in most driving conditions.
I haven't done a ton of driving in the US, so it's possible the situation differs there more than I was aware.