You can't entirely ignore links, because it does in fact tell them what people are talking about and what sites people want to see. The problem is the spammers, and I don't feel bad one iota for forum and blog spammers. The fact is that if people are really into a site (lets say amazon) then, they link to it. Maybe amazon is a bad example, because I know that I just type the site into my browser when I want to buy something (yay amazon prime!). But, you could imagine that x site is becoming more popular, more people are interested in it, it's getting good buzz and people like it. This type of signal is a good way to determine a good quality signal. The problem is the spammers.