Holy muffins. This thread has created quite a stir!
I think it's worth noting that we probably all have a different mental image when it comes to "strollers." When I read the initial post, I immediately thought of the Hummer-style strollers, ginormous behemoths that can hold a couple of kids (or more); enough diapers, formula, and changes of clothes to last through a full weekend; and Mom/Dad's latte, laptop, 4 iGizmos, umbrellas, spare coats, and gym clothes. You know, the ones that take up about as much space as a six-top. (No joke, I've seen strollers that take up more space than my dinner table.) I do think it's inconsiderate to take up that much real estate for stuff. (I think of it as being like taking public transportation to the airport when you are relocating and have four or more giant roller suitcases. I suppose sometimes it has to be done, but I also think most people can come up with an alternative.
However, if we're talking about the kind of stroller my mom used when my sister and I were young, I generally think "no harm done." The stroller was a canvas seat, the wheels, and the handles for pushing. Fully open, it probably had the space footprint of an average adult, and one could sling a diaper bag over the handles. That? No problem.If Mom/the kids could have a seat, it folded down small enough that you could comfortable put it between your knees. I doubt that most people would object to that.
Even in one of the situations where someone has to use a super-stroller, I think they can do quite a bit to avoid taking up aisle space, which is not only inconsiderate to other riders, but potentially dangerous for the kids. If you're blocking the way onto or off of the bus, people will have to scoot around, and even if they are very careful (holding onto the bars, etc), there is a chance that a coat zipper, loose shoulder bag, or something else could hit a child. Many busses and subways in large metropolitan areas have areas at the front for wheelchair parking. If those spaces aren't in use, I think a parent could park the stroller there. It wouldn't block traffic and it is probably safer for the occupants of the stroller as well.