Well, it's not 'just wrong' or 'lazy'.
One argument here is that English evolves - at some stage, chances are, 'would of' will become 'correct'. So in that sense, yes, probably we have to accept language will continue to change.
The other argument is, despite your ignorance, it can be a proofreading issue. Why do you imagine not?
Excuse me for cutting to the chase (I do get sucked into these threads a lot), but to put my cards on the table: I work damn hard to proofreading my posts as and when I can. It is actually quite difficult. Yes, I could easily write 'could of,' because for me, it's a homophone with 'could've' and I tend to confuse homophones when I'm tying, just like a lot of other dyslexics.
If you don't - fair enough. Lucky you.
But why judge people who're disabled? Because that is what you are doing. You may imagine that disabled people will read your nasty, judgemental posts and think 'oh, I'm sure she only meant to have a go at genuinely lazy, poorly educated people, not me'. But I assure you, we don't: we read your posts and we go away and feel shit.
I have three degrees in English Lit, and I'm about to start teaching Oxbridge undergrads next term. I am not lazy, poorly educated or stupid. It wouldn't, in my view, be ok for you to mock me if I were, anyway.
I tell you what I am though: right now, I am feeling really shit because I clicked on your post and it made me feel totally inadequate, because I know I miss-type things quite a bit. So thanks a bunch for that, eh?