Well, he is a part of the Ruby community, and they do often seem to often favor emotional arguments conveyed through harsh language.
Specifically, this comes to mind:
http://lifehacker.com/5859392/swearing-to-make-your-point-a-...
As well as this:
http://www.zedshaw.com.sharedcopy.com/rants/51489cec9386f7c1...
And this:
http://david.heinemeierhansson.com/posts/15-potty-mouths
There are more, but I don't think I need to internet-sleuth the entire set of well-known Ruby / Web personalities to demonstrate the point: a base lack of professionalism abounds.
If ruby-talk, #ruby-lang, ruby-core, and Ruby conference talks were typically littered with swearing, there'd be a point. As it is, it's a generalisation formed off the back of a handful of cases. Stereotyping, if you will.
I've been covering the news in the Ruby world for about 6 years now, almost full time. People are inventing these silly stereotypes as a way to discredit the language and it's users, it's not based in reality.
yOu mAy sAy tHat pEople wHo hAve tRouble rEading sUch tExt sHould jUst mAke mOre eFfort.
But.you.are.writing.the.blog.,.so.surely.you.want.to.be.as.widely.read.as.possible.?.
Postel's law (gently reformulated) is important when you have one-to-many communication. "be conservative in what you send, be liberal in what you accept".