It's not that big a hassle to get a carseat onto an aircraft; you just need to plan for it and arrange your luggage situation accordingly. A carseat satchel or a rolling cart/bungie make it much easier.
I find that dealing with carseats in general is a hassle, but we all do it with cars. Do we do it b/c it is safer, or b/c we'll be ticketed if we don't? If the answer is b/c it is safer, then it follows that it is worth it to use one on aircraft, too, if the child is under the weight recommendation.
BTW, the day before yesterday I was on a British Airways flight that ran into a steady 45 minutes of severe turbulence, and I can tell you there were some really scared kids on that flight. BA doesn't normally allow personal carseats, and kids were bouncing all over their seats and repeatedly knocking their heads against the bulkheads and armrests. DS is older now and doesn't use a carseat on aircraft, but he was hanging on to the armrests with a grip like a vise, just like all the adults around him.