"Maybe I can believe hard enough that bullets don't kill me? Nope. Didn't work." *dies*.

William James, with his pragmatic theory of truth, criticized the dominant scientific view of his time, which held that we should only believe things if we have adequate empirical evidence for them. He argued that many important ways we use belief in society follow a different pattern — in fact, belief can often come first and create the fact afterward.
He gave various examples. One was of a man who believes a woman should love him, and pursues her until she does. Another is from sports, where top athletes maintain a seemingly irrational belief that they can defeat any opponent. For instance, Buster Douglas never could have beaten Mike Tyson if he hadn’t first believed he could. In such cases, the belief created the fact.
His most famous example is that of train robbers, who are able to rob hundreds of passengers despite being only a few men. James explained that the robbers succeed because they can count on one another, whereas the passengers lack belief that, if they resist, others will rise up with them. If the passengers all believed in each other enough to rise together, that shared trust would give them the courage to act — and simultaneously destroy the robbers’ belief that they could succeed.
None of these examples fit the standard account of belief described by philosophers, yet huge portions of society depend on precisely this kind of belief and social trust.

Just once I'd like an imperialist leader to be like "oh yeah I'm doing it because I'm evil. We are the bad guys." But nah they always have to come up with some reason why it's actually good to firebomb babies or whatever.

Caesar, like most brutal conquerors and imperialists, had the additional awkward job of coming up with some kind of reason why he wasn't just an evil monster for killing so many people. He came up with lots of stories about how primitive and savage people like the Gauls and Britons were. Vivid tales of human sacrifice taking place in dark bloody sacred groves were spread around that may or may not
be true. He also claimed they were nomadic (which wasn't really true, plus who cares?) and that they shared their women across many men ("they are doing sex wrong so they have to die" is always a classic).
Probably the funniest one though is that they didn't have cheese. "Cheeseless societies must be exterminated" really shows how the Romans were proto-Italians. Basically the Romans didn't drink milk (they didn't have many cows and were probably lactose intolerant), and thought anyone who did was a savage. "They are eating food wrong so they have to die" is strangely also not uncommon.

Who is wiser after all, the man who refuses to learn about looking good, claiming his ignorance is wisdom? Or the man who, through application of his intelligence and knowledge, has gained the power to dress cool as hell? I think we all know the answer.

Many philosophers throughout the ages have pointed out that fashion is superficial and constantly changing. Probably the most banal and obnoxious thing a philosopher can possibly point out. Thoreau, who might be the most obnoxious of all time, wisely said things like:

I say, beware of all enterprises that require new clothes ... When I ask for a garment of a particular form, my tailoress tells me gravely, "They do not make them so now," not emphasizing the "They" at all, as if she quoted an authority as impersonal as the Fates ... We worship not the Graces, nor the Parcae, but Fashion. She spins and weaves and cuts with full authority. The head monkey at Paris puts on a traveler's cap, and all the monkeys in America do the same.

Five years in the woods well spent, my dude, you've discovered that styles change. Sorry if people told you your weird neckbeard is "out of style" but that's just a polite way to say that no one in any era ever would have thought it looked good.
Thomas More is a bit more interesting, but equally annoying and sanctimonious. He imagines a perfect society in one in which everyone is so wise that they dress as badly as possible at all times. They don't even bother with nice clothes (because they are so busy reading philosophy all the time) and their only use for gold is to us it as chains.
Diogenes is the most interesting for sure, and the most extreme. Where the others give the very easy idea of "boo fashion, it is superficial, not like us!", Diogenes eschews all culture entirely. He strips down main to his "natural" self. No clothes. No civilization. He claims that to live best is to live as the animals do, with our natural instincts.
Hegel didn't talk about fashion much, of course, but when he did he treated it relatively the same as he did everything else. He remarked how fashion, like many other areas of society, undergoes predictable world historical arcs. For example, primitive tribes don't wear any clothes. Then as civilization progresses they put on and more clothes, until a certain point is reached and they start taking off more clothes again. The arc of history creates women's modesty, then slowly removes it. It creates highly formal outfits, then slowly becomes more casual.
I think it's reasonable to think that for Hegel, fashion knowledge producing like anything else, and in the end of history, when the full arc of philosophy comes to its conclusion and all knowledge has been gained, the philosophers of the future will not eschew fashion, but have full mastery and knowledge of it. In other words they will dress cool as hell.

Thales, in the corner: "yes we are going under water, but everything is water, when you think about it, so..."

Those are the engineering vampires you dolt! After 10,000 years of philosophy, you still don't know the difference?

The theory of Occams Razors (plural): the simplest solution to any given problem is often to razor the other guy.