It's quite ridiculous saying these two animals have any resembance to each other. One is a horse and the other is a zebra. Whoever heard of a horse with stripes?

Just because they are galloping around and kicking up their heels...

Just because things aren't identical doesn't mean they don't have things in common. Working out what those things in common are is quite a useful thing to do. The same is true for working out what the differences are.

But unless you do compare them, you aren't going to be able to work out either of those things. It wouldn't really be too sensible to deprive yourself of that kind of information.

It's not really a matter of "Iraq is like Vietnam", versus "Iraq is not like Vietnam". Self evidently, both those statements are true. The interesting questions are "How is Iraq like Vietnam?" and "how is Iraq different from Vietnam?"