You're overly angry about something you either don't understand or haven't experienced. The color of the bubble meaningfully signifies that the existence of that person in a chat is degrading the chat experience for everyone else. As an Android user, it is awful to be in an iMessage group chat, and the iPhone users don't appreciate my presence any more. Basically nothing works properly, and it sucks... and this is by design to create lock-in via network effect.
Imo, the people who have an issue with green bubbles are mostly teenagers trying to fit in. Besides that, its also about how android users can't join imessage group chats, media sent between platforms over sms/mms is extremely degraded in quality, and facetime is a worthy apple service that android users don't get.
If an Android user is added to a group message and changes everyone to green that will be sending over SMS, right? I've not used SMS in a while - does that still come with costs?
Just throwing a thought at your question, I have no opinion on people based on their message background colour haha