Except a lot of those different empire playstyles do add compelling gameplay when the AI chooses them even if they're not ones you'd personally want to play, and putting restrictions on a certain playthrough is a classic way of adding extra depth to an existing game, just like we saw with Purifiers/Swarms.
The purifier civics work because war is a core part of the gameplay, so if you take out the ability to use alliances or diplomacy, there's still plenty for you, the player, to actually do. Whereas if you take away the ability to use diplomacy
and the ability to start wars, then what you're left with is an empty shell of a game because the economy of Stellaris is so painfully underdeveloped.
I've actually tried to play this way in the past, as it's sort of my default method of playing 4x games but
fuck me is it boring in Stellaris. The game simply doesn't have the mechanics support this type of play. Waiting for the game to come to you is the one way guaranteed to give you an absolutely terrible Stellaris experience. What you get is the exact experience that very negative Quater to Three described - waiting around for something, anything, to happen
Honestly, just because this feature isn't for you doesn't mean you need to go on a crusade about it.
Four posts is a crusade now? OK!
If there's something else you want added/fixed maybe post about that rather than wasting your time talking about a feature that, judging from the reactions to your post, is pretty clearly going to be appreciated by some people and may even be quite popular for people who like to play tall pacifist empires for at least part of their game.
I dunno, maybe make it so playing tall isn't heartbreakingly tedious and unrewarding? Maybe make the planet management actually has some depth to it, so the thing you'll spend most of your time doing as a pacifist hermit kingdom is actually fun? It's not rocket science.
Now, personally I'd make it so that instead of saying you *can't* start wars or form alliances, you can but you pay a heavy price for it - maybe 2 influence for an alliance and a massive unity/unrest hit from starting wars so you can sort of do if you really have to, but it's really hard to pull off. But that's not the main thing, the main thing is to make internally focused gameplay actually fun, until then making a civic that requires you to focus on the least interesting part of the game seems like the height of madness.