You almost certainly should, and if you’re scolded for it you probably work for parasites. You’re not wrong to hide that activity from them but I hope you’ll find a role where contributing back is valued not chastised.
If you build a software and because of a bug it breaks something, that is fine. If you deliberately change a library to make any software running it crash and you know it is used among other things by software that control nuclear plants or elevators, my guess is it will probably considered a crime in most juridictions. This regardless of the fact said software makers should test their changes.
I was taking a naive view from a theoretical point.