I'm glad I was taught good grammaer too, icy, and I think kids should still be so taught.
But one can think those things and still accept that writing things as spoken, especially on social media, is hardly a big deal and, in any case, doing so can be part of being "in" when you're a teenager.
Secondly, people do not always take in what they are taught. Those who haven't are the ones who make mistakes that they aren't aware of.
So long as writers of broadsheet newspaper leader and comment articles, and writers of good books can write well and grammatically I'm not going to get to hot under the collar about mistakes made by the proverbially great unwashed.