There is one thing that I don't get. Rodney McKay has made three separate attempts to create a power source superior to the ZPMs. In one of those attempts he destroyed at the very least an entire planet, and in another, he almost destroyed a galaxy in another dimension.

It must be because the writers want the story to go that way, but the problem that he needed to solve was the problem of creating a brand new ZPM. I remember some speech he made about how it was more dangerous to try to new way. Why not do it the old way and have ZPMs on hand? I know, it might make some things a little too easy, but it's beginning to look pretty dumb.

I don't remember the speech to which you refer. But if you're accustomed to the standards of rigorous scientific explication in sci fi literature, you just have to abandon them if you want to make peace with sci fi movies and TV. Just look at how much disbelief must be suspended to watch a regular drama or action show or movie. "Oh come on, a real cop would never do something that stupid."

This isn't even "rigorous scientific explanation." It's overlooking the obvious, something they have to do to make plots work sometimes, I guess.

I don't think he has any idea how to make a ZPM. He just keeps stumbling across other methods of generating power that seem like they might be "even better", but turn out to be disasters.

Maybe it's yust the plot that they don't gave enof power. Didn't he once blew up 3 of those things to destroy a other city? Surly that city would also have been destroyed if he yused unplugged them, without it's shields it's interior whould be exposed to space. So the inhabitants would also have been killed/forzen.
Annyway Atlantis has a bid of a "plot what plot?" problem. What exactly happend with that medievel city for instance, and why didn't the team relocated to here, why didn't they shove that ancient in that girls face that stores a working zpm for ancients and why doesn't that doctor has any ethical problems with what he's doing

Not having any idea how to make a ZPM is a good excuse. I had assumed that he knew enough to make one since he knew enough to make the "more advanced" type that had caused so much wreckage.

I remember an episode in which he had to drain a ZPM to take away the power of a ruthless family to rule a village. I don't remember him ever having to detonate one. Detonating one can take out an entire planet or even a solar system.