Has been for many years now...
And again, how is that not affecting player agency? Literally at least one player loses their entire character because of your decision to insert your CE PC into a good aligned party!
First off, you're making a very big and not-always-correct assumption that the rest of the party is Good-aligned.
Most of our parties tend to average out at Ng or Cg, so maybe small-c small-g overall. I can't think of a party - and I've seen a crapton of 'em both as player and DM - where every member in it was some form of Good. There's always at least one Neutral (of some type) and sometimes an Evil or two.
That said, it's probably worth noting that two playable classes in my game - Necromancer and Assassin - cannot be Good and will in general at least trend Evil; and a third class - Thieves - are rarely Good. Given that, and given that Thief and Assassin are pretty much the only available options for sneakery and locksmithery, it's hardly surprising that an all-Good party is a rare sight.
Right now the party I'm running with my wife as the sole player is probably as Goodly as I've ever seen - mostly due to the adventuring NPCs in it. Yet they're not all Good - her two are N and Ng; the N sometimes has a tinge of e to it, and one of the NPCs is also N.
You're not just stripping agency, you're negating it entirely.
Same could be said when a PC perma-dies due to an Ogre or Giant or 1000-foot fall; or loses its mind and can't function any more; but this is never brought up (and nor should it be!).
The only difference is the source: the DM and-or game world, instead of one or more other PCs. The character's still hooped either way.
A DM that allows such a thing is failing in his duties as a DM.
As far as I'm concerned a DM who disallows such things is failing in her duties as DM, which are to present the game world impartially and neutrally and then referee whatever the players/PCs decide to do with it or to it.
What strips away agency is when a DM tells me what I'm allowed to play and-or how I'm allowed to play it, when other options exist in the setting. By this I mean if the setting has no Elves I've no right to expect to be able to play an Elf, but if Elves are a playable creature and Evil Elves exist in the setting my agency is impacted if by fiat I'm not allowed to play one.
Not that it's any guarantee I would play an Evil Elf in this case. It's the principle of the denial of options I'm fighting against.
If you want to play some kind of Dark Side Sith Necromancer Murder Rapist, wait till we play an evil campaign thanks (and we have the consent of all players for such a campaign and character).
Hyperbole aside - Dark Side Sith Necromancer Murder Rapist...really? - I as a player should have no say whatsoever over what you-as-player decide to play, and vice-versa. In fact, ideally I shouldn't know what you're playing until I meet it in the game.
And if we end up playing incompatible characters, so be it - we can sort it out in character in the game, probably involving the other PCs in some way*, and we'll either find a way to work together or we won't. If we don't, them's the breaks - one (or both) of us will soon enough be pulling out the roll-up dice.
* - even if their involvement consists only of placing bets on who stays/lives and who goes/dies.
DnD is a co-operative game, and a group game. No-ones fun or enjoyment should trump anyone elses right to the same.
It's a group game, in that it usually takes a group to play it; but nothing says it has to (always) be co-operative, particularly in the fiction. Sometimes co-operative is fun; other times it's boring. Sometimes individualism is fun; other times it's boring. And each player's tastes on/for such things will inevitably wax and wane over time - the co-operative goody-good PC that has you brimming with excitement today might bore you to death in two years, but in two years the campaign's still got many years yet to go......