If the whole world is pulling backdoored gems off a compromised Rubygems.org, panic seems like a reasonable first reaction. This isn't the Rails bug; there was nothing to be gained here from secrecy.
You can never be too sure. There's a whole contest (http://underhanded.xcott.com/) whose goal is "make something that looks legit, but actually does something evil / has an exploit).
Nuke from orbit.
It is better to be paranoid about it and get the word out before someone actually gets hurt. If the users get to it before the maintainer gets to it, at least someone got the word out.