I don't know anyplace on the web that you can have a polite discussion about anything. There is, of course, ExIsle, but you have to watch your Ps and Qs or run afoul of the Great Golden Book of Rulz. In other words, no curse words, no personal jabs, post not poster, except if you are a liberal commenting on a conservative's post (political discussions in OT). But, you will find many other civilized topics under discussion there. They, too, are having problems with keeping/attracting membership. Right now, for example, a link was provided for free onlilne college courses.
Most forums are just a repeat of junior high school: bullies, jocks, princesses, nerds/geeks with a sprinkling of those who just keep their collective heads down and try to search out something to engage their minds.