I've taught in 4 different educational institutions, including large classes of SEN students. I'm not talking about mistakes made by those who genuinely don't know they've made them, or typos. I see these mistakes from those with 'good educations' and no learning disabilities. In that context, laziness is an appropriate assumption. I do not judge people on this basis but I do wonder why they value their language skills so little.
Generally the people who make genuine mistakes don't mind being corrected if and when appropriate.
I'm terribly mathematical challenged and if someone corrects me then that's good - there's right and wrong in maths for obvious reasons. There's also right and wrong in English and although the reasons may seem less consequential, they are still important, otherwise why do we teach it in schools?
Whilst marking academic essays my superior told me to mark foreign students down for poor English but not those who had perfectly good English skills, yet chose to write in slang. I refused and marked them all according to academic guidelines. Some had quite obviously just submitted awful work and then not even bothered with spell checking. I'm not sure how that can be excused if someone professes to be serious about their education.
Language is no different to appearance as a signifier of intent, so we should arm ourselves with knowledge as much as we can surely? I think we're all able to tell when poor language/literacy is a product of poor education and when it's just laziness.