Bad spelling, grammar, and English in-general is a virus. The more people get lazy and don't bother, the more it's spread around and seen by others... who then in-turn become further de-sensitized themselves to it. This affects their own usage, and it propagates further.
What's worse is that people will 99% of the time respond, "oh I know better, I just don't bother". Except that after a while, they DON'T know better anymore. They become so accustomed to bad spelling and grammar that it permeates even their formal writing where the "I know better" part should've kicked in... but doesn't. Now they look like idiots.
I'm sorry... but if you want to be taken seriously, you need to not write like a 20-something who spells like a 1st-grader. There/their/they're. To/too. its/it's. Your/you're. "Couldn't care less" vs the nonsensical "could care less". And so on.
It's not being a "jerk" to give a shit about the quality of English writing and trying to preserve some semblance of sanity and education to written communication.