Titles can be useful, present AND absent
Let me sidestep to a different realm for a moment: I've usually found that finishing a freshly written email with a usable Subject: line does improve the message as a whole. Viewing titles here as much the same, I'm not opposed to them, though their function is slightly different -- titles don't have to introduce the message before I can read it whole, and they can sensibly continue into each other.
Regarding writing titles, especially in the beginning I'd be at a loss for a title but with a suitable arsenal of placeholders this is no longer a problem. Regarding reading titles, seeing how the no-title-complaint message ends up as a title and I find myself reading that in full, wasting my time, not requiring a title and making the line vanish when empty might be a useful experiment, at least.
So, long story short: Sure, go ahead and make titles optional.