Just to add to it, I believe they are not only allowed, but also encouraged by theymos. He said something about shill accounts being useful for free speech or such. It is somewhere around the forums.
Can anyone share a link for that? 
Here you are. https://bitcointalksearch.org/topic/theymos-please-ban-all-common-ip-sockpuppet-accounts-104178
I don't have a problem with alt accounts as long as they're not used for evading bans. If you're hesitant to say something controversial because you don't want it to be associated with your name, please create an alt account and say it.
If there is something you're not comfortable saying associated with your name, maybe you should reconsider saying it at all.
That's a pretty naïve view, IMO. A person isn't composed of just one personality. You're a different person in different places and situations, and it's uncomfortable to mix all of these personalities into one.
I think there is a more serious point here. You can use sock-puppets to create false credibility, such as positive feedback on a fake investment opportunity. You can then use that credibility to con people out of their money.
I sometimes do react to stuff like this when I see it. Readers should really judge posts purely on the merit of their arguments, though, and not based on how many people said something or how many posts someone has.
