It's considered illegal because it's chucked under the same realm as spoofing. Even spoofers have bonafide orders exposed to risk but "intent is not for the orders to execute." It's basically pro-algo/HFT/MM bullshit regulation.
So where does that leave my real-number example above, where a MM's algo just leapfrongs my 10 x 0.65 Bid with its own 10 x 0.70 bid (in a somewhat transparent attempt to make me pay a higher price...possibly even getting hit by the same MM's selling algo if I go to 10 x 0.75)?
I don't think it's inaccurate to say that the MM's doing exactly what, if I'm understanding correctly, you're saying it would be illegal for a retail trader to do?...That is: submit a quote whose purpose isn't necessarily to get executed, but rather to entice retail buyers to bid higher? I suspect I already know the answer...? That it's just one of those things where yep, unfairness and all, the individual investor is getting screwed by a regulation that penalizes him for doing something MM's are allowed to do?