Imagine in 2010 you meet a potential romantic partner and they say, "Hey! Add me on Facebook!" And you reply, "Oh, I'm not on Facebook... can we just talk on the phone instead?" The person may go, "Oh, umm... sure, I guess." But then you never connect because you haven't made it as easy as possible; you've introduced a tiny amount of friction that a lot of people are just not willing to tolerate. If everyone else is on Facebook, why aren't you?
In real life, it creates so much friction that yes, there is pressure to buy an iPhone and change your entire software ecosystem just to fit in and remove this barrier to relationships. It's just text messaging; it's ancient technology at this point and no company should have a monopoly on it in any form. At a minimum they should let other operating systems download iMessage—show them ads, charge a fee, I don't know. But creating a hardware-enforced wall around basic telecommunication is wrong.