Did Google really say that? It makes sense to treat it as a different category of link. An organic back link from a blog or website is putting the weight of the website’s name/reputation behind it whilst UGC has users putting their name/reputation on it (as it relates to their relationship with the originating website). The latter is not worthless as the website ultimately allows it, it not as strong as a signal as an organic backlink.
I’m not comfortable with any endorsement being inferred toward any link that is UGC, even from something the website tacitly “allows” by not deleting it. For the majority of websites there’s plenty of absolute trash lurking in all the Les travelled parts where nobody cares or nobody has seen it. But the bots will always see it.
