Nobody is saying to just let Kyrie walk at the end of his contract or just trade him for scraps. The major trade returns I have seen include: Kawhi, AD, KAT, and the #1 pick. There are a very select few who would trade him for less, but these are what people would want back in a Kyrie trade.
I bet most of the people scoffing at such a trade are the same ones who couldn't believe we would trade IT/Crowder/BKN pick for Kyrie in the first place. I don't think we should trade Kyrie because it would paint a pretty bad picture (but not as bad as if we trade Hayward). I am also excited about a future with Kyrie as our PG - I am just a little bummed we are going to lose Rozier for much less than he is worth (or nothing).