Bias is important for credibility of a source, but not for the validity of the argument presented, and for the latter you actually have to understand and think about the argument presented.

The most important part of that page is its argument that all states wield authority and tend to tighten or relax the exercise of that authority in order to serve a given set of class interests. There’s nothing in this that relies on credibility, and dismissing it on account of bias makes as much sense as responding to someone in a debate by saying “you’re biased, so why should I believe you?”.