I'm actually not opposed to people selling them. However, I'm generally opposed to entities coming in and buying up every whatever it is they can get their hands on to force a shortage for individuals (for example, bot networks buying up concert tickets faster than individuals can).
I'd totally encourage someone (and have) to sell their reservation to another individual who has genuine interest in the vehicle, even at my own expense. I literally did that this week, I was talking with someone that was thinking of cancelling theirs, and was willing to pay a reasonable amount for it. They got another offer that was significantly higher than mine, and I happily encouraged them to go get take that offer.
My opinion here is also informed by paragraph 14. It's fairly clear (to me) that Rivian does not want to encourage scalping of the trucks, but has tacitly ignored/allowed transfers of reservations between individuals without supporting it (they will not proactively swap reservations for people). If it becomes obvious that people are selling or buying reservations (as OP seems to be doing) just to resell them, I expect Rivian to attempt to crack down on that. So I think there's a balance here that the community probably needs to make in self policing.
Now if you have a reservation, and go through with it, and then decide "hey this isn't for me," sell it to whomever. You took delivery with intent of receiving the vehicle, and then decided to move on. That's normal.