The fact that international calling and texting can cost a ton of money when I can message someone over the internet for free via wifi is nutty.
Your problem comes from that fact that Apple cleverly introduced way more capability in the very same Messages app, for other Apple users only.
None of the complaining like yours would be happening if Messages was left as SMS only and apple had shipped a separate iMessage app, which is exactly what Whatsapp is. But there's Apple's forte. They have Bluetooth, but buying Airpods automagically works better.
I also 1000000% guarantee you that the designers spent a LOT of time analyzing the green bubble colour to make very it a slightly (but not too much) aggravating green. There are many many more pleasant shades of green.
Edit: OK yeah, a designer explained it here: https://uxdesign.cc/how-apple-makes-you-think-green-bubbles-...
What you want is for Apple to be forced to extend its proprietary system to non-Apple systems, but when you say it like that it's obvious what an unfair nonstarter it is.
Paying for SMS messages, when it costs phone companies literally nothing, is what should be illegal.
People who are not you care if messages are encrypted. And reply differently when threads are available. And so on.
I don't see any issues when sending SMS from iOS to Android and vice versa.
Google has Messages, which does the same, i.e. handles both native and SMS messages, and is only available for Android.
I suppose the same is true on Android if people use their stock messages app? But what drawbacks does it have when messaging an iPhone user? I've never heard of any problems (I don't use that app) but I hear about the differences iPhone users experience all the time.
There are no differences with iPhones, other than the green bubbles. On the other hand, Google Messages tags SMS with "Sent as SMS".
The issue is purely based on aesthetics, if anything. Green versus blue bubbles. But there are really no interoperability issues with iMessage handling SMS.