It's misleading to just say "because of the green text" it's so much more than that. If you have an active iMessage chat and users are using iMessage features, it's a weird experience for the non-iMessage folks. It seemed like a real victory to have emojis in the UTF format, but of course now Apple turns on the big FU and finds other ways to chide non-iMessage users. Don't blame the kids.
The kids could just be inclusive and switch to Telegram or WhatsApp or even Messenger. But the kids want to discriminate — humans, particularly Americans, thrive on excluding other people. the kids are just imitating the patterns they pick up from adults.
Try finding a recent US-produced music video or hit movie/TV series that shows a green bubble (or Android for that matter, as it still has a higher market share).