Perhaps this teacher was looking more for thoughtful analysis and insight rather than pedantically seeking out minor grammatical errors.

Call me archaic, but schools should teach proper spelling and grammar in addition to the process of reasoning. I can't take any writing seriously if it's done poorly. (I didn't think the essay was done poorly though, it's still better than a lot of writing done on the internet nowadays)

You are archaic. I _almost_ said 'your archaic' there. Grammar, spelling and punctuation are often arbitrary rules that are difficult to grok, except with extensive experience with them. One of the best ways to discourage that experience is to make everything about everything and mark down an otherwise-excellent essay due to spelling.

Note that I am not saying that we shouldn't teach those things (and schools do teach those things), but that teaching them in a lower-stakes fashion where people are able to succeed at the core learning goal (argument in this case) without bouncing off of the Wall Of Spelling is a much better approach.

Meanwhile, from two comments earlier:

'more influentiable people would be like "Oh wow I can totally get rich selling drugs as long as I don't startg using it myself!"'

...

Well it seems fitting for a great old one to be archaic...