Suit yourself, but if you refuse to learn basic grammar you will be treated like you are stupid and uneducated. Like it or not, presentation matters. Getting the basics right, including things like spelling, grammar, etc, shows a basic attention to detail without which your services will likely do more harm than good.
actually it's "etc."
(I wouldn't usually be a pedant, but if you think the difference between "--" and "—" matters, you should probably try to get the basics right too.)
https://www.merriam-webster.com/dictionary/etc even redirects to the correct URL with a "."
This is all stuff you learn in school. Punctuation isn't obscure or niche. You may not have learnt about semicolons or em dashes in school but you should have and I did. As did anyone that has ever read a novel. There are two semicolons on the first page of the first Harry Potter book, a novel read by approximately every child of my generation. There are loads of examples of the proper use of dashes and other "obscure" punctuation marks in any professionally typeset text.