I'm relatively new to the EN World forums (Hello!), and it's interesting how different the culture of the boards here are. When the OP discusses an optimized character, people immediately launch into a discussion of how mechanical balance is important. Given the amount of D&D I see around here, I suppose that's not surprising: D&D is often about a team of heroes working together, with careful balance required for the pre-fabbed encounters to work properly (it is possible to balance an encounter for wildly different power levels, but it requires careful customization rather than grabbing one of those intricately designed monsters from the monster's manual. No surprise then that you see more people, for example, advocating wildly different power levels on the SJGames boards than here).
But I think this discussion has missed something vital in the OP's post:
Firstly I'd like to state that there are all sorts of optimisations. I am not talking about the gamebreaking builds that you see on charop boards, I'm simply talking about making intelligent decisions about your character's choices.
*snip*
And yet I constantly find that I'm penalised and punished for this behaviour. Not only this, but I also constantly encounter the Stormwind Fallacy, whereby people believe that just because I bring a well-made character into the game, that I can't roleplay or that I won't have an interesting character history.
The problem here isn't that his character is "too powerful" for the group. The problem is that he has people looking down on him, essentially, for "roll-playing rather than role-playing" or some such nonsense.
Here's why I personally think this happens: Early RPGs (and many RPGs today) had... problems. The mechanics of the game often didn't match up to the fluff of the description. A great example of this is Conscience from Vampire: the Masquerade. Vampire is all about waxing angsty whenever you accidentally killed someone and seeking redemption, and according to the fluff, a character with lots of Conscience really values his Humanity. However, mechanically, Conscience prevents Humanity loss whenever, say, murdering little old grannies, and sufficient loss of Humanity results in loss of character, therefore, logically, if we wanted to play a character who murdered lots of little old grannies, we'd need a high Conscience (and likewise, if we played a character who really clung to his Humanity and never violated its tenets, then you can get away with a very low Conscience).
You have, broadly speaking, two sorts of people that'll play a game like that. The first sort will see that, according to the fluff, his angsty vampire who values Humanity should have a high Conscience, or that a jerk vampire would have a low Conscience, and stats his character accordingly. He's using his stats to describe his character. Another player, someone like the OP, would look at the logical consequences of what the stats actually do, how the rules actually work, irregardless of what they say they do, and will stat his character according to that logic: A humane vampire with low Conscience and a vicious vampire with high Conscience.
I can list a litany of games that have these problems, from 7th Sea that actively punished you for taking anything that gave you character or let you buy into the setting, or Scion, which punished you for buying anything other than Legend.
The problem with the latter player, the smart player, in the eyes of the former, the descriptive player, is that he's carefully outlining just how broken and screwed up their system of choice is, which is a pretty unforgivable sin. When you show the Vampire ST just how messed up Conscience really is, especially if he hasn't figured this out on his own, he may react by shooting the messenger. If he already knows, this might result in a second sin: The players might realize that this game is totally broken, but have a sort of unspoken agreement not to push the system. They'll build their characters according to the fluff, nobody will build them in such a way that they exploit the huge, gaping flaws in the system, and everyone gets a long great, right up until someone bulls in and tears up the delicate, tissue-paper thin bandaging they've placed over the system.
There's a lot of games where this isn't a problem (and those tend to be my systems of choice), games that reward you for emulating the genre the game is trying to create, and veterans of those games might not realize that there's an entire swathe of players out there that enjoy evocative-yet-broken systems (like Scion, 7th Sea or Vampire: the Masquerade) despite their dysfunction, and accidentally cross lines they didn't know existed. And even if you're not playing a game like that, there's a strong chance that you're playing with a group that has come to resent characters who are built with mechanical competence in mind simply as a knee-jerk reaction from their days of playing such messy systems.
Or so has been my experience.