I've seen a few comments recently that start with:

This is specious reasoning

It's an insulting phrase and from now on I'm immediately down voting it when I see it.

On the face of it is insulting, until you dig a little deeper

> It's an insulting phrase ( ...)

I'm sorry you feel like that. How would you phrase an observation where you find the rationale for an assertion to not be substantiated and supported beyond surface level?