I did think the implication was obvious, but that was an assumption on my part. I agree that a statement like "if you can't talk right don't talk at all" could be very problematic (and could easily be referring to, say, anyone who speaks with an accent or in a particular dialect, anyone without perfect grammar, anyone with a speech disorder, etc.). I apologize for being unclear.

What I meant to say is: if you can't express yourself without saying things like "that's so gay", "don't be retarded", "he/she's acting like a bitch", etc.--if you're using slurs or terms for a marginalized group in a way that implies those groups have something to be ashamed of, whether or not you mean it "like that"--then it's time to zip the lips and open a thesaurus. I'm all for disagreement, but it's possible to disagree with someone (politely or vehemently) without using ableist, racist, sexist, or transphobic language.

Dehumanizing and casting aspersions can be done easily in polite terms
That's definitely true. I didn't mean to imply that the use of certain "bad words" was the only problem here, 'cause that would be woefully oversimplifying the issue. I'm sorry I didn't word my comment more clearly.