Why is cross-posting bad?
1. The OP doesn't consider where would be the best place to post, so they broadcast:
2. It feigns urgency, by hoping more people will read it sooner rather than later:
Trust me, when you've seen your answer posted by someone else on another forum in reply to the same question a few times, the novelty soon wears off.
I REALLY hate having my time wasted by selfish cross-posting snowflakes thinking theirs is the single most important post on the web right now.
And it's dead time - time which CANNOT be used to help someone else instead, because it was wasted repeating what has already been said.
So yeah, whenever I see cross-posts, I put the cross-links in.
And no, this isn't for the benefit of the OP, no matter how much they whine about being called out.
It's for the benefit of the regular helpers, who can quickly check whether what they were thinking of saying has already been said elsewhere.
Of course, the cross-posting OP might soon get tarred with the persistent cross-poster brush and routinely ignored on all forums - which is a bonus.