The amount of spam and nonsense already exceeds many many lifetimes of all researchers that ever lived combined, so unless you can demonstrate the current generation for some weird reason does read a lot of extra published nonsense on the arxiv, the practical impact of the change in ratio is still 0
Not sure why you upgrade to a much broader "net negative" point when you can't even defend the much more narrow "publishing nonsense somewhere wastes a lot of valuable time"
I think that researchers, educators, and others with power over institutions & culture publicly lampooning and attacking anyone with even the thought of daring to ask a 'dumb' question or have a 'dumb' theory, without proper rite of passage and standing as a crackpot has a larger negative effect than whatever positive effect these attacks have in dissuading (probably not!) the delusional and fraudulent from stuffing people's mailboxes with their theories and amassing followings.
Political thinking that probably predates the Egyptian pyramids: If you empower people with freedom, it will be abused in a way that produces some suffering for everyone that wouldn't be had the freedom not been granted. There would definitely be tradeoffs to having a culture of free and open learning, research, and knowledge sharing, unguarded by institutions.
