Hoaxers simply disrupt scientific progress. Imagine people bombarding SETI radio antennas with fake signals just for fun.
I, on the contrary find them extremely useful. Oftentimes they expose the overall gullibility of the UFO crowds out there, including several "authority" figures in the scene. It's a good thing if it makes people think a bit.
That is, when the hoaxes are admitted or otherwise debunked. I think we can rest assured that a lot of hoaxes remain unadmitted, hoaxes that don't provide enough information for them to be decisively debunked by a third party, and thus remain "UFOs"...
There are lots of people out there that find it immensely satisfying to fool someone, and who don't see any incentives to "come clean" about it.