The equipment is rated for a reason, and when used correctly, a single-rope system SHOULD be sufficient. However, for those a little less trusting in the equipment, I understand the people who would prefer twin ropes.
I'm comfortable with the equipment, and using a single rope system, as between the two I simply gained more exposure to it, and don't use things that don't pass through safety checks.
People on these forums seem to bash on a lot without necessarily providing reason or justification, just "you should all think the way I do". Funnily enough, it is quite easy to get fired up and respond in kind without taking the anonymity factor with a grain of salt.