Fantasy is always consensual; the line is only crossed when people share these images. It's the difference between fantasizing about a co-worker and telling them about those fantasies.
The problem is, this service very publicly shares those images, and usually in a way that directly tags the actual person. So, very much across the line in to "harming actual people."
Since this regularly harms women, people round it off to "misogyny". Even if the motive is not "harm women", the end result is still "women were harmed".
(There also IS an exception if you know the person well enough to expect that they're cool with it - but the onus is still on you if you guess wrong and your actions end up causing harm.)
The problem is, this service very publicly shares those images, and usually in a way that directly tags the actual person. So, very much across the line in to "harming actual people."
Since this regularly harms women, people round it off to "misogyny". Even if the motive is not "harm women", the end result is still "women were harmed".
(There also IS an exception if you know the person well enough to expect that they're cool with it - but the onus is still on you if you guess wrong and your actions end up causing harm.)