Some people pay per text message received. So, they have to ask each and every one of their iMessage-using friends to please not send these ridiculous reactions, because they are ultimately another text message which will cost money. If that counts as "forcing others to adapt their communication" well then I'm sorry, but their preference is my cost, so I don't think it's out of line to politely ask them not to.

Ultimately, this is something that I'd rather be handled at the carrier layer: I should be able to have my phone reject a text message and not pay for / receive it.

On the topic of configurability: Software should ultimately serve the end user. When a developer makes an undesirable (to a user) change to the software and provides the user no way to opt out of that change, it's serving the developer's interests, and it's doing a slightly worse job at serving the user.