Some people think it's "just how things are done on the Internet". Some know it isn't OK and don't care. They do it anyway. Some actually think you ought to just be fine with their posting whatever they want on the Hub you may have written with an aim toward producing high-quality information/writing, or that you may have written with the idea that your Hub may actually help someone (and sometimes in a meaningful way). Basically, they're oblivious to the concept of solid, meaningful, writing; or else they think anyone who isn't "takes things on the Internet too seriously" ("because, after all, the Internet is all about trying to get traffic for yourself").
Then, too, there the people with their agendas when it comes to wanting their own opinions heard and spread around. That's another bunch who aren't interested in YOUR Hub - only their own agendas.
Either way, delete the foolishness you don't want on your Hubs. These clowns don't care if they make your Hubs or HubPages look like a big "spam fest" or "link fest". (In fairness to some of them, some actually don't know any better.)
It only really takes a few seconds to go down your list of comments, scan for any links, hate speech, profanity, etc., and delete any/all of that stuff before dealing with the comments (both positive and negative) that add something to your Hub. The way I see, it's an "every man for himself" kind of thing. Those people are "for themselves". I'm going to be "for myself" (my Hubs, my reputation, my earnings, etc. as well).