I'm with "canon is important to worldbuilding storytelling" and that it matters (and is personal) what rule is broken and how far (and if a reason is given, and if that reason is valid), mostly in terms of "did they have to do that?" I hate it when it seems they don't.
Most people would be pissed if the whole ST canon from TOS was scrapped (Hence the "Kelvin Timeline")... especially if there wasn't a compelling reason given or cause shown. They are at the idea that This new timeline means that people and events we've known and loved for years was all a "oh but that was all a dream/it all happened in a time loop/alternate reality" situation.
I think this has to do with what defines ST (or any story) to people. If everything about it was changed, then would it still be Start Trek?
For those who don't think they have a problem with canon, well, what if TOS wasn't internally (mostly) consistent? What if, in every episode, rules, aesthetics, roles, entire characters etc were changed, without explanation (except they want to tell some story)? One day Kirk's captain, next it's Spock (not because he took over, he just "always was"), then neither is even in the show, and it's no longer about space exploration, it's a colony, SF doesn't exist, it's the Vulcan Alliance we're observing...
Might be fun (def is in Twilight Zone and Outer Limits for ex).... but it wouldn't be ST.
Like-- Trills cant use the transporter or it will kill the symbiont. In Ds9, Trills use the transporter all the time without any damaging effects. And that is besides their major appearance change. No explanation.
A little rationalization balm: It was never "a fact" that Trills couldn't transport, it was just what Odan said, at a time when SF was not aware of their joined nature, so maybe he was trying to keep the secret (certainly the transport would've shown two lifeforms etc).
It is also never explicitly stated that the hosts are Trill... they are called Trill hosts... but that could mean they are hosts to a Trill, not themselves Trill, or could refer to them being representatives of the Trill, not from Trill (as in not indigenous to Trill). Or maybe there were a different race of Trill.