Backing in as a concept isn't the problem. The problem is when people who clearly don't have the skills to do it try to do it.
Backing in shouldn't take any longer than pulling in forwards - if you know what you're doing. There's no need to constantly pull out and straighten up if you get it right the first time and do it in one smooth movement.
And of course, those people who aren't competent at backing into a space probably aren't going to be any better at backing out of it either. So, one way or the other, they're going to hold someone up. Either they back in and hold someone up and drive out quickly, or they drive in quickly then hold someone up later when they're backing out.
So, no. The backing up isn't the issue, or what holds people up. What holds people up is inadequate driving skills.
But it's not rude to have inadequate driving skills. And I've been known to inconvenience people when I'm pulling *into* a parking space head-on.
I think it can be, actually, if you're subjecting other road users to them, depending on what those inadequate skills are.
I think we're basically in agreement - it's not rude to back into a space, at *all*.
But if you try to do it, knowing you won't be able to do it without holding people up - in other words, backing up, pulling back out, straightening up, backing in again, pulling out to straighten up some more because you can't do it right the first time - does that then make
it rude? Because then it's starting to veer into rudeness to me, or at least obliviousness.