I don't know what to say...
And I know that some people do not like or agree with that reasoning, but it's one of my reasons for limiting powergaming, because powergaming is about one's own fun with no consideration to the fun of other players. After that, there are tons of various degrees, and some people powergame and still respect the other players, but it's still a selfish consideration at start.
All funs are selfish. People take pleasure in different thing. What would be selfish would be to stomp on other peoples fun, being disrespectful, etc. But playing a certain way, whether it's being a theater kid in costume, enjoying building a really efficient character with some cool abilities, or exploring a fictional world and being focused less on your character and more on the setting, they're all valid. As a GM, you have to find a way to accommodate different types of fun. The more there is in your group, the harder it will be. But approaching the game from a power gaming is not more selfish than other ways.
No, it's not. Playing casually is just that, whereas powergaming is putting special effort into making a selfish difference in the game.
Powergaming is not more selfish than spending weeks writing a backstory and sticking out your past at every roleplaying opportunity. There's players with bad habits in all gaming styles.
And all the better for you if you can consistently play with only like-minded players. However, it's not always possible when playing with friends, even old-time ones who know each other by heart.
The exact same could be said to you in relation to how you play. All the better for you if you play with open-minded players, but if you play with strangers you might encounter people that enjoy different aspects of the game.
And don't even try to pretend that it's to explore new roles, I very much doubt that you have tried all the archetypes of all classes even in the PH.
Oh boy. Multiclassing absolutely allows to explore new role, and it allows you to do things that the, in my opinion, very limited class/subclass system of 5E doesn't allow. It's also a great way to reflect change in a character, a Fighter that takes interest in everything nature related as the campaign progresses and decides to put a few levels in Druid. I'd be much more excited by one player coming to say he'll dip in a second class than a player saying "this time around I'll play this subclass instead".
And I'm sorry, but if you allow them all, it's because you want powerful characters. Most of the feats (and in particular those used in these builds) are only there for pure technical power, they have nothing to do with the story or the roleplay.
Multiclassing can be used purely for its technical value, but it's not inherently that way. You're one of the most binary people I've seen online. It doesn't have to be one of the other. In your mind, it's impossible to conceptualize that a DM could allow these options without wanting more powerful characters. It doesn't make it reality.
And again, on this, I am speaking from experience and I suspect that you are not. I have started D&D in 1978, and we were already really roleplaying at the time, almost as we are playing today. So no, it was not grafted over the game over time, it was there right at the start. Moreover, it's been more than 40 years for me, but more importantly (and again powergamers don't like this pointed out), it is the way all recent editions and in particular 5e are described by the designers. And 5e has been in existence for about 7 years now, so no, roleplaying is the basis and the intent of the game.
Esh. Aside from the very condescending tone of your message, everything you're sharing is anecdotal. You having played this way for forty years as absolutely no impact on the conclusions of a discussion like this. You can't make any facts out of it. For people like you, there's someone that focused on getting gold, magic items, building powerful characters with little roleplaying.
So here you go, whereas rules and rolling dice are not the best thing in the game, it is a roleplaying game first and foremost, so it cannot, by definition, destroy the game like powergaming can

p, see there is a smiley there).
This feels like when of my coworker argues me that my hershey bar is not a chocolate bar but a candy bar because it's written on the packaging for legal reasons. You've quoted like five sentences from various editions as a proof that these games were designed one way, and should be played that way.
I haven't played anything before 3rd edition. And you're right that every edition from 3rd to 5th does mention and encourage roleplaying. But you're buying a set of books that total multiple hundred of pages, and 95% of the stuff inside is rules, options, magic items to get, feats, etc. What you're buying is a technical framework with technical content, there's no rules for roleplaying. Most editions, aside from a few sentences in the opening chapter and a two-page spread example of four people roleplaying, say very little about roleplaying.
I'm
not arguing that roleplaying isn't an important part of D&D. It is. Or at least it is for me. But if there's one rule that trumps anything you could quote me, it is that no two groups play this game the same way. There's no "core" or "true" D&D experience. Even the designers themselves have said that they made some changes and don't play everything as per the rules. All kind of people play these games for all kind of reasons, they're all as legitimate and they're not more or less
true what what you consider the basis of D&D.
It seems to me like you've spent 40 years playing the same way, and you're so entrenched in your way of playing that you cannot fathom people playing differently. You'll allow them to. But they're going against what
D&D is. They're being selfish. They're just interested in technical options.
And at our tables we chose to leave them just like we do with other options, and not ask for advice because we are not building technical characters that need a technical crutch to seem attractive to play.
Once again, it seems impossible for you to conceptualize that someone could both spend time to build an efficient character and roleplay. But these things are not mutually exclusive, I'm a man of both crowds. I will scour books for options and build optimized character. I like when my DM sends us some really tough challenges and I like overcoming them because I've built my character well. But I also voice my character, I write an extensive backstory, I force myself in doing some in-character choices. Things are not binary. Stop trying to push your view of the hobby as universal and absolute facts.