While all of you ladies are 100% correct in what you say, the unmentioned benefit of these things could be convenience. Assuming they're affordable, and are put together really well (i.e. very realistic lady parts), it becomes a matter of hassle. It'd be a lot easier to go to the closet, man cave, or some other secret chamber to whip out the doll, pop one and then go about his day than to go online, look up potential prospects, determine spending amount, narrow down selections, availability pending, how soon, weather, and one or two other things.
Even if many guys had one of these things, at some point we're going to want some real pussy again. However, this doll may narrow down HOW MANY times guys are willing to go through the hassle. A guy who hobbies 20 times a year may reduce that to 10, because he's banging his doll every other day or whatever.
I love real women as much as the next guy, but if I can pull out my doll, pop one off in 10 minutes vs spending an hour showering getting dressed, driving, etc to make an appointment happen, many times I may take the easier road.