All of these things are known, and the REASON they use rats. If you want to study tumors, you need something that is relatively likely to get a tumor. What they're looking for isn't "Did rats get fat" or "Did rats get tumors". What their looking for is, "Out of X number of rats did MORE rats get fat, or tumors or whatever, when we did Y than when we didn't do Y.

So if, left alone, 10% of rats get tumors, but when exposed to 30 minutes of Glenn Beck/day, consistently 25% of rats get tumors, that's unlikely to be just because "rats get tumors".

There's nothing wrong with basing conclusions on studies with rats. There's something wrong with ignoring parts of the results that don't agree with your conclusion.

I guess I am just biased because I have pet rats.
I do see your point about the conclusion.