I also don't really think the 'created roster spot' argument holds any water, because a) where one team gains two spots, the team they're trading with loses two, so it's zero-sum in terms of teams rostering waiver trash, and every eliminated already team has multiple guys they'd drop in a second if they saw something of any interest on the waiver wire. Dinger has at least 5 guys with zero chance at having offseason value that he could have dropped if he saw something he liked. These two new spots hold no value to him.
The strong reaction people are having to this seems equal parts visceral "I don't like this because it feels like it might be a problem", and butthurt because teams with nothing to do are making deals and playoff teams feel like everything should pause so they don't miss out.
I'll reiterate that I don't really care, because I can't really be bothered to talk trade right now, but I just don't understand the opposition, at all.