Not so much regional, but yes, there are some vocal MNers - alongsidesome very vocal members of the general public - who have strong rage around accents and dialects that are different from what they're expecting, and IME, it's getting worse recently on here and elsewhere.
In the last year, I've had far more people get aggressive that I have a mixed accent with some words clearly not local sounding than ever before. I've been shouted at work about "That's not a local accent!" when answering question, I've had quite a few get really annoyed when they ask how long I've lived here if I say that I've lived where I do for over 20 years as they seem to view it insulting that I don't sound perfectly local - I've had the desire to bring up that Arnold Schwarzenegger has lived in the US longer than I've been alive and still sounds as he does, but never yet had the energy to come out with it to anyone who pulls this.
I've been told on here that still having such an accent after so long is a failure on my part, and that's certainly how it seems people have started reacting towards me in the last year or so - not only my failure, but that I should just accept the abuse as punishment for failing to sound local. I'm at the point now where I no longer answer questions about why I sound weird, I openly say I'm not comfortable discussing it anymore or just walk away when I'm asked. I've given up trying to be polite to people who care more about how I sound rather than the content of what I ay.
spelling and grammar are right or wrong, they don’t have a regional accent.
Standard spelling and grammar for Modern English didn't really start cementing until the late 18th century, and Standard English is based on the accents, dialects, and ideas around language of those who developed the texts that then had the power for them to become the standard. Even with that, spelling can show accents - see Mum/Mom/Mam - and as writing online tends to be more in-line with how people think and talk rather than Standard English, it often shows dialects.
If you were brought up with RP as the standard, then certain things in common usage, eg, “aitch” pronounced “haitch”, are incorrect.
I see those as two different ways of saying it. I don't see either as incorrect. I don't see the point of putting that kind of value judgement on something like that.
Just because we're brought up using language a certain way doesn't mean we need to view other ways negatively. That's a choice.
so there has been a genuine concern about the Americanisation of "holidays". Which in itself is an American phrase.
Holiday comes from Old English and regularly used to refer Christian festivals for centuries. It was in British English that it became expanded to mean any time off work, religious occasion for any faith and certain secular occasions as well like Bank Holidays and New Years. The earliest American texts I'm aware of followed the latter part significantly later. It may be more popular in the US now, I don't think that makes it an American phrase. It, like many 'Americanisms' is a Britishism that either fell out favour or was never used in wealthier parts of England and just ignored that it's used in other parts of the country or the Anglosphere well beyond and was brought to the US.