Uh, well...yes.
Getting a book published on anything is a major accomplishment, be it on puppies, wrestling, coffee, socks, aardvarks... I have a great deal of respect for just about anybody who does this. Doesn't mean I agree with them whole-heartedly, but I respect the drive and persistence it takes to get this done. Trust me, it ain't easy.
As for Moore, put aside his politics for a minute and think about what he did--went from some lard BUTT nobody in a dead American town to becoming a filmmaker, author, activist and in some circles, a respected political critic. That is not an easy thing to do.
Any wanker can post on a message board about anything. Only a handful of people can convince a publisher to cough up money for a book about their opinions. Getting to that point takes *some* degree of talent.