Does repeatedly careless spelling and total disregard of grammar justify criticism?

In a recent answer to a question, another @Fluther wrote, “Fluther… is notorious for being grammatically snooty and spellingly snarky”.

We all make typographic errors and sometimes even on rereading we may miss an error. I’ve done it and I appreciate being cut some slack for occasional errors.

I use the spellings used in most English speaking countries. I use the “u” after the “o” in words like colour and behaviour. I recognise (US: recognize) that most Americans don’t and that is fine with me.

When a question shows no knowledge or concern for spelling or the rules of grammar, I sometimes lose interest in answering the question unless it is an excellent one.

If someone’s answer shows the same disregard for the reader, I will disregard their answer unless it seems to make a powerful point on which others have not yet touched.

Occasionally, I will correct the writer, hopefully without rudeness.

Are we snooty and “snarky” about grammar and spelling.
Are we justified in responding to the errors?
Does it raise or maintain the level of discourse.
What’s wrong with setting and expecting an effort towards maintaining high standards?