Users install Ubuntu, have a problem, and are directed to Ask Ubuntu. It is a boon to Ubuntu users that they do not then have to go through a registration process to get help. It's a strong message that the Ubuntu community wants to make getting help and using Ubuntu as easy as possible.
Furthermore, Ubuntu is supposed to be an operating system for everyone. Even people who aren't Internet-savvy and might have problems even registering an account. Where are they supposed to go for help then?
So should we change this policy? Should we require everyone to register before posting questions (and answers)? Well, if the current way is not achieving the goal of helping people, then we should. If not requiring registration is actually making it harder for most newcomers to use the site to get help, then we should change this policy and require registration.
I'm not aware of any evidence of such a trend, though it's possible.
But I am concerned at the attitude that we should change the policy because it bothers us. This is a minor annoyance. Not having to register to ask and answer questions is one of the most notable positive features of Ask Ubuntu, compared to other resources. Unless and until we have real, strong evidence to show it's severely backfiring, it would not be appropriate to require registration.
Furthermore, there are other ways of fixing this problem. The underlying problem seems to be that getting accounts merged is too hard. This problem is known to Stack Exchange developers, and a fix for this is intended:
We need a simpler mousetrap.
Going forward, the sanest thing to do is offload as much of this
responsibility as we can for merges to the users that need them, and
improve our own facilities to handle what should become exceptional
cases when the system can't process their request. At that point, we
can just put the option back in your grasp and continue to handle
ourselves whatever the system can't.
See full answer by Tim Post for more information and context.