> When did it become socially fashionable for anyone to disparage another for her choice of programming language?
My first instinct was to say 1957, when FORTRAN came out; but there were probably earlier instances after assembly languages came out that people still hacking machine code were disparaged for not switching.
> Competent programmers write efficient and stable software in the languages they are most skilled at using.
I don't think so. Competent programmers know the art of picking a reasonable tool for the job; e.g. unless you really need to use something else, write Android programs in Java. Not only that, competent programmers in real life have to work with other programmers; you may be the best ML or Modula-3 hacker in the world, but if someone else has to work with you or will have to maintain it after you, those probably aren't the best languages to use.