As I think about it, I think lowering the barrier to entry does generally ruin things

The internet is worse off.

The sports I participate in got cheaper to start with and are worse. Cultures worse.

What has gotten better because the barrier to entry is lower?

Of course this is true but seems to be one of the most underrated facts of modern society. Always it is proposed without question to expand access to things, to "democratize" them, open barriers, open borders. But this invariably lowers quality while crowding out those already enjoying them. Think of any quality club, park, vacation spot, restaurant, online forum whatever: none of these are improved for your own usage of the thing by adding more people to it at least beyond some threshold. A lot of this is zero sum, and quality is in tension with quantity.