Scared of Your Own Words?
It is way too easy to post on a spur of mind, and not carefully consider what you say. I guess if you know this is how you are then an alias might be a good thing to use.
On the other hand, if you do change aliases, you won't have any background under your new alias for others to view your comments against. If you are saying something obvious I can certainly use my own judgement, but I also find it useful to read others opinions for the purpose of expanding my own views. Before I'd feel comfortable about adopting anyone's opinions I would like to get to know them (e.g. on the net by reading what they've posted before).
Now maybe I should go and search for myself on deja.com to refresh my memory on what I've said in the past... :-)