I mean, that’s absolutely a fetish in a general sense. I might even say it’s common, even, considering what I know about female erotic stories and the like. I’ve found an almost certainly female author making stories about women cheerfully getting mind fucked into someone just as powerless to resist their owners as a shrunken women is, and a sort of shared universe literally called ‘Human Domestication Guide’, where the main characters are made into obedient pets by invading, well meaning aliens, so… yeah.
If you’re into it, willing, and consenting, then it’s not ‘unwilling’ in the meaningful, rape-y sense, which is rather the point where that gets awkward, morally. Hell if it’s just a story or a fantasy, then there’s no one real at all to be concerned about, and RPs aren’t real (unless you’re actually shrinking? 😏 ) so even if a ‘giant’ ‘steps on you’ you’re not actually getting stepped on by a giant foot, so… what’s the harm?
Honestly, I’ve always found it more concerning the other way around, since then you’re actually doing the wrong thing. The same logic applies there, of course, but I’ve always had problems emotionally accepting the logic about my own desires, so it’s not like I don’t get what you’re talking about.