I don't think it is appropriate, and may be considered offensive; particularly considering that the post itself is about the Perch CMS.
I think you have a point to say that discussing alternatives is perhaps is better on another post/thread.
However to state that it is not appropriate to discuss alternatives to Perch simply because this is the ‘Perch’ forum is strange. It’s a public forum about Perch. Everyone on here are developers, who use Perch to develop websites.
While I personally don't agree with perhaps the tone and aggressiveness of some comments, for many (myself included) Perch is not currently meeting their needs, and that is after a very long period of time waiting. Hence the discussion of alternatives.
I've talked on WordPress forums about preferring Perch, I've seen intense discussions of pros and cons of alternative CMS’s on many other individual CMS forums. No one there thought it shouldn't be discussed.
It could be worse… we could all just leave the forum and Perch and not come back. The fact we are discussing alternatives here, means Perch is still figuring in our calculations.