I don't want to use the default Android SMS app, because apparently it will soon support sending and parsing iOS fallback messages (i.e. 'Liked "..."'). I just want plain, standards-compliant SMS, with no risk of accidentally sending fallback messages. Plus, I don't agree with the notion that Apple should be able to bully others into recognizing their SMS extension features.
If doing so wouldn't require any proprietary code, then why do you think that's a bad thing?