You don't "pick" a diverse audience; you respect the audience/fandom how it currently is. I refuse to believe that if you surveyed ANY fandom and asked them to do a character description of the main character, they wouldn't come to a fairly common consensus overall.
>which is, like, accidentally racism.
No it's not, it's people saying the character isn't as they expected them to be - and again that's on the person using the franchise to match what they are creating to that built-in audience FIRST and FOREMOST - if they don't want to respect that audience they shouldn't be touching the franchise they should be making something original.
> I refuse to believe that if you surveyed ANY fandom and asked them to do a character description of the main character, they wouldn't come to a fairly common consensus overall.
Even if the consensus is wrong? Jesus wasn't white, and wouldn't be described as white, but everyone in the US 'fandom' thinks Jesus looks like them. Also, Jesus is frequently portrayed differently in different parts of the world.
In Twilight, the main character is not actually described very well. There's an old comic from the oatmeal [1] about how the main character should be named "pants", because they're made just so that every reader can slip into the place and pretend like they're the main character.
This is a lot more common in books than I think you may realize. So when characters don't match expectations, it's because people are saying that characters don't look like them... which is, like, accidentally racism. To be clear, I don't think people are doing this maliciously. It's just that what you expect is not necessarily what you have to get.
[1] https://theoatmeal.com/story/twilight