We've never taken a hard line that any deviation from canon is always bad all the time. One of the fanworks most celebrated in the PPC is The Official Fanfiction University of Middle-earth, which takes Lord of the Rings characters wildly out of character for the sake of comedy. Jay and Acacia even use OFUM's "Elrond out of character" as an assassination method in their sixteenth mission.

The reason OFUM can write all the characters OOC and still be considered good is that it knows exactly what it's doing and why. It was written with full knowledge and respect for the canon in mind, but respect doesn't mean strict adherence. There is always room for a writer's unique perspective in fanfiction. That is, indeed, the point of it. If we weren't open to that, we wouldn't read fanfiction at all.

And it has always been the firm stance of the PPC that anything can be written well. That includes non-canon slash pairings. What we take exception to is bad writing, especially when performed in willful ignorance with no respect for the original.

We are also well aware that subjectively enjoying something that is objectively garbage is a thing, and we don't shame people for it.

That you seem not to know any of this means you are quite far from being in a place where you'd be granted Permission, so perhaps worry less about that and more about actually learning who we are and what we're about?

Also: "swore to destroy"? Dude. It's just fanfiction. We're here to have fun. Calm down, aye?

~Neshomeh

there is no black and white when it comes to this issue. There's a difference between an interpretation of canonical character or element that might not be 100% accurate, and flat-out getting it wrong. See example about Gandalf randomly marrying a girl he comes across.

To use a musical analogy, you don't always have to play a piece exactly as the composer wrote it. You can change the key, the tempo, arrange it for a different instrument or style, or occasionally play a note differently … and all of that is quite different from mashing random keys on the piano and turning the piece into unrecognizable cacophony.

have I become the very thing I swore to destroy when I joined the PPC?

Nope! I got into M/M when I started watching Hetalia waaaaay way back, and since then I've been into a lot of M/M ships in other fandoms, canon or non-canon.

Getting into non-canon ships is fun! Writing fics to enable non-canon ships is very fun! But that's why at the PPC it's the Department of Bad Slash and Het, not just slash or "non-canon pairings". Characters should retain some amount of their original personality regardless of who they're dating.

So no, you're not going against some unspoken PPC rule for liking non-canon pairings. I might adore Bilbo/Thorin and Legolas/Gimli (and believe you me I did not ship Legolas/Gimli when I was younger), but not everyone here likes those ships as anything other than platonic. That's fine, as long as we respect one another.