I will wade in to the Unformedness Wellness of Aggregators debate only long enough to offer the following :

People are going to write bad feeds because, well, we're stupid that way. Tool-makers are going to accommodate them because if they didn't their software would violate the Fridge Principle which says you just plug it in and it works. Rather than wasting a lot of cycles trying to socially engineer either camp wouldn't it just make more sense to provide low and high level libraries that perform the function equivalent of Tidy for syndication feeds? That way a tool-maker can simply plug it in to their application and get on with doing cool stuff rather than writing tag soup parsers. It ain't the purest solution out there but, frankly, whatever. If you really care that much you can write a patch for our imagined libtagsoup that collects data about bad feeds and send them to a centralized database which can then be polled for use with friendly evangelism.