what if I have no problem with either form of toplessness?
Then you also realise you're outside both cultural mainstream and the general consensus about behaviour in public places present in all countries of the North. And many of the South as well
Which brings a little to the subject itself.
Unless... someone sharing your opinion argues that breastfeeding is fundamentally different kind of nudity, free of indecent conotations, just because... society thinks so. Which is debatable anyway.
unfortunately, you fail at understanding that just because some people derive sexual arousal from something doesn't mean that it's inherently sexual. If it were the case you'd have to forbid being barefoot in public too, to only name the most obvious example.
I'm neither advocating bannig bare feet, nor accepting ad absurdum point of view. Apparently, particular society made it's own set of rules about which part of the body is considered indecent. For some reason breast-rules seem to be rather detailed and enforced harder than feet-rules, so also for some purpose naked breast is considered indecent, while naked foot is not. You're welcome to explain this weird case without "sexual" theme if you wish to do so. But "Millions of people are simply misinformed about what should be considered inherently sexual" version is acceptable only if we treat sex purely as a reproduction tool. Anything else about it tends to escape such artificial borders and nobody even needs any marginal "philia" to explain why. There were times when public coitus was something close to mandatory in western cultures - so society rules are indeed shifting a lot and I doubt you'd expect the process to be rational.
So I'm not afraid about "ban everything" case. Not going to happen, even Taliban failed at this field.
But as I recall OP asked something along the lines "is it ok NOW?" - not hypothetically (feet case) or always (coitus case). If we're talking about the society capable of going partially insane after some ridiculous "breast accident" (Janet Jackson?), there's surprisingly little to talk about.
Me? Don't really care, both arguments have valid points, though I prefer a little predictability when it comes to the rules. So in societies where public topless is considered indecent - be discreet*. No cherrypicking, no pitiful militant groups bending the law with their campaigns, less double standards - the better. Special circumstances? Treated like such, not as an excuse for everyone else.
* How to determine in which society you are? Common sense - but when still in doubt, stay on the safer side. Sure, it's bloody unfair, but such rule would be golden in waaaay more serious social problems, so I see no point in avoiding it in such cases.