In many ways, it is true.

Where it can be an issue is when a debate turns to a question on logic and philosophy, and depending on the intelligence of the person you are debating, the argument you are arguing for has to be pretty sound. Logic and philosophy are only as backed by your "faith" in it. If you do not truly believe in something, it will become harder and harder to defend it.

Don't get me wrong, I play Devil's Advocate all the time merely because I don't like the arguments that people put against many issues (whether I support the issues or not). Most people aren't smart enough to take me to a scale of logic that I can't keep up with (i'd say all, but that is against Quantum Physics).

But I don't think I'd be able to argue in favor of Collectivism against someone like Ayn Rand. I'd have to use bad reasoning to support Collectivism in the first place. Works against simple people, but not intellectual elites like Ayn Rand.

It encourages a deeper thinking, and strengthens agruments

I hardly ever believe in one side. I usually think both sides are nuts and try to come up with a third alternative. As a matter of fact, I even go so far as changing sides half way through the argument ;)