I haven't run into it much but that's because I don't do things with the local homeschool groups (yet). I suspect I'll run into it though.
There are homeschoolers who are very rigid about the curriculum they follow - they use grade books, etc. themselves within the curriculum they're following (not all homeschoolers, but some) - IMO we're not that different from those homeschoolers, in the end. And in fact, many of us are quite flexible about the components of our curriculum (the example of me doing Christmas music for the music lessons springs to my mind) .... it is true that once they're a certain age, they'll be taking the state tests etc. If we're still doing k12 at that point, and I feel like their "Study Islands" are taking too much time away from actual learning, then I may reposition myself. But, right now, I've got a pretty flexible curriculum which came FREE, including the computer and much of the extras we use (ie tempera paints etc.) --- so I'm happy with it.
I suppose it's not that different from the Mommy Wars we encounter in other areas -- the whole judgmentalism about whether or not mom works at home or outside the home, or eats organic (or not), or whatever.
ETA: I do think that there is a concern that these virtual schools were established as a way to control homeschooling more (that is, to get public schooling into the 'homeschool' business, and begin the argument that THAT is what homeschooling should be, rather than parentally driven homeschooling). And also as a way to siphon homeschoolers back into the public school system. However, I think that virtual academies appeal to a different type of homeschool parent -- there are plenty of mothers here who started with a virtual academy and switched to straight homeschooling. It's as likely that parents who might not have considered homeschooling, would try a VA, and then decide that they could do full-on homeschooling. It could go both directions (and I suspect would lead to more moving to full homeschooling than not, in the end; I like k12 right now but am not convinced that I will still be using it in 3-4 years, at least not with Ina?! We'll see....)