Not unpopular at all.

Yes, I was taught to always hold the door. I will hold the door for you if you are even ten, twelve or fifteen feet back. It is polite to hustle a little if you are at that fifteen foot extreme

How in the world could it possibly be view as polite to expect someone else hustle because of your own personal weird quirk?

I see people hold the door open for strangers all the time, so it doesn't seem unpopular to me. In fact, I can't remember ever having someone let the door close on me when they know I'm behind them.

Honestly if I'm more than a couple of steps behind them I'd rather catch the door or just open it myself than feel pressed to hurry while they wait for me. I appreciate that they're being considerate to me though.

For others, I'll hold it open if they'll be at the door in a second or two but not if it means standing around or pressuring them to hurry.

Depends on the location I guess. Here it's mostly done and since it doesn't really take any effort I would agree a look behind and holding the door is something everyone should do.

This should be a matter of course in general interaction with one another, as long as one is not physically impaired. Just as one does not stop in the middle of the aisle in the supermarket or block it with a shopping cart. People are becoming increasingly inconsiderate.

Yes, that is one of the most stereotypical polite things that exists.

If the person is directly behind me, I'll keep the door open while simultaneously walking through the doorway (I don't stop and wait) so that the door at least doesn't close in their face. They still have to grab the door to prevent it from closing though.

I really don't like standing still and holding the door open and making the people who were behind me go ahead of me. And I hate when someone does that to me. It feels like a very antiquated and patronizing gesture.

Luckily this is not being discussed everywhere. There are still places on Earth, where this is totally normal, a sign of good manners. I never care who the person behind me is. I hold doors for everyone and I do it the way they do not feel they have to rush.

Why unpopular? I do that all the time without thinking.