I think there's a lot of positive aspects about the subgenre as defined: Being rigorous in the approach to writing SF, sticking to probable futures rather than improbable ones. In fact, it doesn't seem new to me: Wasn't the New Wave all about sticking to mundane themes? Haven't many SF authors been doing this all along? Just yesterday, Jim Gunn and I were discussing this, and he said, "Pretty much everything I write has fit the description of mundane SF."
What bothers me about the mundane-SF notion boils down to its perceived attitude that writers working in other subgenres of SF are being lazy or just tossing in existing tropes like confetti rather than using these elements to tell stories they can't tell using the mainstream (heretofore defined as "mundane") literary tropes of everyday life in the here-and-now.
Granted, many authors use SF tropes without thinking them through, using them only as stage-dressing (see Lucas as our tale's primary villain). But I don't think anyone in SF has been advocating that as a solid approach to writing. Certainly, the subgenre of hard SF has always strove (striven? *g*) to be rigorous and to test their theories before deploying them into fiction.
So the mundane-SFers seem to be setting up a straw-man argument. That's what bothers me about it.