Witness data is binary signature blobs. Its expensive to abuse, hard to parse, and ignored by most tools. OP_Return is explicitly indexed and human-readable with basic tools. This makes it a low-cost storage layer for junk or worse and can seriously damage bitcoins reputation. I think there is also a serious distinction between a node that decides to propogate this garbage, and a node that is forced to store it while giving a best effort not too. Intent matters

Eric, Yes, I understand that. Which is why this has become such a contentious issue. If in some universe it came down to requiring a hard fork I’d have faith in knots on principle. I’ll vote with my nodes, I don’t have to be held to core’s requirements to push that data into the tip with my nodes and data. I don’t understand why a select few wish to push these changes other than to monetize spam. It seems rather antithetical to the ‘bitcoin ethos’ on a number of principles.