If you're worried people will be disappointed when their ancient thread necro doesn't result in responses, I think people are perfectly capable of seeing that a thread has been dead for a long time. I strongly suspect that all the 'people' in GD with registration dates after 2018 are actually bots.
If you think necroing threads is actively harmful, I don't see how. A zombie is better than a corpse. Nothing is more harmful than inactivity.
(Sidenote, I don't think changing the default cut-off will have any impact.)
The outraged poets threw sticks and rocks over the side of the bridge. They were all missing Mary and he felt a contented smug feeling wash over him. He would have given them a coy little wave if the roof hadn't collapsed just then. Mary then found himself in the middle of an understandably shocked family's kitchen table. So he gave them the coy little wave and realized it probably would have been more effective if he hadn't been lying on their turkey.