So you put these all in the same category: gaining knowledge, gaining abilities, and just obtaining things.

I gatekeep my bike, I keep it behind a gate. If you break the gate open and democratize my bike, you're an idiot.

I'm not sure how you're getting that from their post? None of the four things mentioned (book publishing, web publishing, open-source software, computer hardware) involve stealing someone's property, he's saying that the ability to produce those things widened and the cost went down massively, so more people were able to gain access to them. Nobody stole your bike, but the bike patents expired and a bunch of bike factories popped up, so now everyone can get a cheap bike.

it is more like:

You gatekeep your bike, you keep it behind a gate, you don't let anyone else ride it.

Your neighbor got a nicer bike for Christmas, rode it by your house and now you are sad because you aren't the special kid with the bike any more, you are just regular kid like your neighbor.