Lulu I don't know if you've noticed but that is the point of a discussion forum. People disagree and debate. The vast majority of people come here knowing, wanting and accepting that people will disagree with them. Coming on a site like this is tacit agreement that you accept that. There's no such similar feeling about grammar because this is not a spelling and grammar site and no such expectation of correction is assumed.
If you put £50,000 for a costing of £80,000 in you would be an incompetent who hadn't made basic checks on their work, could potentially have caused huge problems for your work and probably deserved to be sacked.
If you are being examined for English you need, of course, to check and recheck what you are writing and ensure it is correct.
But for some random person on an internet site to insist that what they read is treated with the same kind of attention to detail as a work based report or an examination environment is the worst kind of pomposity resulting from an over inflated ego and sense of self importance.
Which I think is what the grammar pedants need to realise. Their irritation means zilch in the great scheme of things. Nobody cares, it adds nothing to the discussion. Anybody who can't see the difference between a web forum and examination English is obviously also somewhat lacking in the ability to tailor their writing to an appropriate situation anyway, so they probably shouldn't be dishing out writing advice in the first place.