Lower the amount of reputation needed to comment
On SO, I think that this limit does more harm than good; comments in this thread make some of the points I'm about to here.
Namely: it is very confusing to new users who would like to participate in threads but perhaps are not comfortable providing an actual answer. Furthermore, it encourages the wrong behavior on the site, since some users will (with no other option) post an answer to the thread with something that would normally be a comment. And then they get admonished by other users, which is just a bad feedback loop all around for something they should be able to do the moment they sign up.
I've heard the argument that this is to avoid spam comments and the like; I don't really buy this since they can post an answer into any thread they want from the first moment.
I'd be curious if we'd be willing to try this to see if the spam quotient is as bad as was believed when this capability was first put into place. I wonder if there's an actual problem here or just a perceived one.