The thing that someone who has a firm grasp on an issue will often find is that most people on both sides don't actually know what they are talking about.
I think the first time I really realized it was when I was drifting away from my religion of birth, and actually started to listen to atheist people around me. I soon discovered that the only difference between most of them and the religious people I know was the value of $religion variable. For one group it was "God", for the other it was "no God". The thought patterns were exactly the same. Neither of them could actually justify their beliefs.
I don't think this is very true--what significant/majority of religious thought patterns are the same in atheism? The only one I think you could make a case for is ingroup/outgroup thinking, but that is not a majority of religious belief.
Acquiring the belief because it's popular in your ingroup, along with a strawman-based view of the outgroup(s). No real effort spent on thinking the belief through; lack of any real argument against the beliefs of the outgroup(s).
Most people are complete morons when it comes to anything they don't have to deal with on a day to day basis. They know what they need to know to continue existing any maybe they know or learn enough to get ahead but beyond that people are generally ignorant and clueless to their ignorance.
For example, I personally have a stake in the gun control issue. I'm against "banning assault weapons" because I'm against a bunch of bureaucrats having a chance to define "assault weapon" because last time we gave them a chance they banned a bunch of things that make firearms look scary. Ditto for background checks but to a lesser extent. Existing implementations suck, a lot. The same goes for tougher laws in general, they don't seem to have done much of anything for the positive and there's anecdotal evidence they may be negative (look up some of the pro-gun number crunching exercises f you want an example). Why would I or anyone else who wants to go to the range want to encourage more of this? We see it as the firearm equivalent of security theater.
However people who aren't well informed on the details have had these two carrots danged in front of them as a cure to a problem in our society and they'd be fools not to reach for them when they're framed in that context. Meanwhile they can't be bothered to wonder why anyone wouldn't want these things. After all, some poll says $large_percent of people support $thing, yet they can't be arsed to even wonder why that $small_percent is holding out.
You find this sort of problem on both sides of any controversial issue.
> "Stupid" implies that they make bad choices after being fully informed, which is often unproven.
I don't think this is a particularly universal definition. Willful ignorance that negatively impacts your own understanding of the world has always seemed to me to be very reasonably defined as stupidity.