There's also the fact that if a person has absolute power, no matter how they exercise it or how noble a person they believe themselves to be, they can not do it without forcing their will on somebody and becoming a villain. Riker with Q powers would be like Gandalf with the ring.
Um... I don't really think so. Unless someone does obtain Q like powers in the real world and we see how much it affects that person, who is to really say that absolute power will automatically turn you into a villain?
The idea that "power corrupts" is not an absolute and this episode doesn't give any good examples on how it could corrupt Riker. All Riker does is try to make things better. The very fact that he acknowledges and takes everyone's wishes back shows that he is capable of dealing with his powers in a responsible manner because he's being respectful to the crew's wishes, i.e. their will. That alone to me says he's more worthy of those powers than Q is, but this episode says he shouldn't have those powers period because.... it didn't corrupt him?
Also, the Gandalf and the Ring comparison is not a fair one. The Ring is evil! It is literally designed to corrupt and taint any individual who would wield it for themselves for the sake of one day getting back to it's proper master. It has a will of it's own. Riker's power does not.
And if god like powers is such a bad thing, why does Picard gloat about how humanity is so freaking awesome that we will not only become gods ourselves, we might become more powerful than the Q? If Picard believes we're so freaking awesome, and Riker learns that he should use his power responsibly, what's wrong with continuing to have said powers so that we can show off to Q that humanity can use our powers in a sensible way?