I can wrap my head around the usability and interoperability arguments but this idea that "social standing" is contingent on iOS vs Android just seems alien to me.
Are there really people that adjust their social circles based on what type of phone someone is using?
Additionally, when you first make the switch (at least circa 5 years ago), any iPhone-only group chats you were already in will need to be restarted (with some care taken by each iPhone user involved), otherwise you will not receive those messages because iOS will continue to treat it as an iMessage on others' end. It is very easy to miss out on communications this way, and from there it's not all that hard to fall out of touch with people who weren't closer friends to begin with. Either you need to be proactive or your larger social circle needs to be thoughtful and/or really like you.
So with all these issues, there is a bit of extra work involved for everyone when Android phones are involved. Some circles are so iPhone-heavy already it would be a little awkward to be that guy making the whole chat green. Couple it with a false perception that Android coincides with lower socioeconomic status (obviously not true for certain devices anyway) and it's easy to see shallow people being petty about them. Plus less tech literate circles just accidentally excluding people and you get a real fear of social hurdles.
Your wording suggests it's an active decision where they immediately cut someone out because the communication turns green. And for some, it is an active decision. It's a common "joke" to poke fun at people for making the bubbles green too. But the more insidious way it arises is like how you might see patches of grass dying off due to shade and eventually turning to dirt. Someone sends a meme or a video or a picture to the MMS friendgroup, no one can see it as it was originally intended, so the iPhone users create a "sidechannel" (way easier than moving to an entirely different app) iMessage group where they share the memes and videos. Eventually the culture between the MMS friendgroup and the sidechannel friendgroup diverge until they no longer associate. The blue grass grows while the green grass turns into a patch of dirt.
Not social standing per se, but a 0.01% chance of being excluded isn't going to feel good.
One friend in a group chat has an android, and that hoses the messages I send out, because Apple will default to SMS. It is quite maddening.
The main complaints from other seem to be about high def videos, pictures etc, which I don't personally care about.