I consider having several (independent) mirrors to be a benefit for the community, because such distributedness assures more reliable accessibility of your public work, now and in future (it will survive the failure of any single hosting site).
That's why I want to keep track of the available diffeent options to publicly host open-source projects:
- Which public hosting sites for darcs projects are there?
- Which public Git hosting sites are there that are free software?
I believe it's rather ethical (or moral) to put some effort into ensuring that your public work is published in the most accessible way (well documented, and with some guarantees about it being accessible at any moment when someone is interested).
The effort for you to push your work to several places independently (I mean, they won't depend on each other) and manage all this is probably not really a nightmare (as suggested in some other answers here), especially with a DVCS. For example, one can even set up Git so that one pushes to several places with just one command.
I feel that unless you are forcing someone to read something done by you, but you are rather just putting your stuff somewhere for it to be findable and accessible if someone is interested, you are not egoistic or ego-whatever.