Although I do not support the fork and don't think it is possible to eliminate spam, I'm still of the opinion that the BIP's proponents have a point in pointing out that large, contiguous chunks of data might pose a legal attack vector, as opposed to fragmented data. It will be hard for node runners to claim plausible deniability if illegal material is embedded in a well-known format (like raw jpeg) in well known locations (OP_RETURN outputs). I haven't seen a serious attempt to address this issue (maybe I'm not paying attention) and I don't think it can be disregarded easily.