I mean, I think saying they 'intentionally' damage it is probably a bit strong. Are they as careful as they should be? Probably not. Remember back in the day watching a news story where NW (yes, so this is old) handlers were basically throwing around luggage like they were basketballs. It's not like they were intentionally throwing things to the ground to break them - but yeah, would not want my things thrown around like that for sure. I suspect they just don't care - individual handlers probably don't actually care much about airline responsibility or not, as its the airline dealing with responsibilities and I think unless there is a pattern of damage long enough that they can specifically figure out the employee was responsible, I doubt there are much repercussions.

IME, through two kids and dozens of flights on UA, have never had a gate checked stroller or car seat damaged - at least beyond what I'd call wear and tear. Though we always put them in protective bags designed for the purpose, so never gave the stroller/car seat completely unprotected to any airline. I'd recommend that to anyone traveling with strollers/car seats, mind you, anything anyone gives to an airline.