Valid points being made on all sides here. And, yes, in one sense they are only uniforms. Yet, on a sociological level, they're part of the social fabric that creates unity among strangers.
But let's be real with each other--uniform variety exists solely for making money off of fans. It's what's left of capitalism in a debt-based economy when the actual manufacturing of products with inherent value has been traded away. All that's left for Americans to sell today are trends and fads and "intellectual" property.
We are now where war-depleted, socialized Britain was in the early 1960s, as skewered by the Beatles' George Harrison in "A Hard Day's Night":
"Of course they're grotty, you wretched nit! That's why they were designed! But that's what you'll want."
When I was young, our "assault on sports tradition" was wearing white cleats instead of black. Drove my dad crazy! Every American young person since the 1870s has gone through a similar phase, and by the time they're 30 or 40, they are embarrassed by their earlier ideas. I'm not yet 70, but every style of clothing I've worn since grade school has now been "in style" thrice! (Sometimes I think obesity is a plot by the fashion industry.)
Speaking now of things much more important than clothing or team uniforms... what I'd like to remind the younger fans who love variety is that what makes tradition (in any realm) valuable is the number of decades it takes to build a tradition, and the short time it takes to destroy it. It's like a successful long-term investment account. Its value accumulates over time--but if you withdraw early, you lose the great benefit you had earned.
We can all agree that when tradition ceases to be functional, then it must be changed.
But if you diminish something that took decades to build merely for the sake of novelty, you can't just "rebrand" tradition again when the novelty of novelty has worn off. You're only left with memories and regret.
Variety for the sake of novelty is not a healthy place for any mind or society to be. Sometimes your elders dig in their heels on something silly like uniforms, because what they're really worried about the more important traditions in life that they see being plowed under by design, not free choice.
For all our crankiness, what we wish more than anything is to pass on to following generations the joys and opportunities we enjoyed, that we see being taken away. But that's all complicated and intellectual and hard to articulate. It becomes much easier to just yell, "Stop screwing with the team colors!"
...and stay off my lawn!" (which is still the traditional green for valid, scientific, and widely beneficial reasons.)