The suggestion to read books doesn't sound to me like suggesting people avoid critical thinking; quite the opposite.
"Riddled with bias" doesn't make sense to me. Any book - one about maths, as much as one about the world - is written from a point of view. This is the "bias" that phrases like "riddled with bias" seem to suggest can - and should be - completely eradicated. But the decision what to include in a book, what to exclude, for example, is a personal one. (It's why committees have a bad name.) All we know of the world is how it appears to 'biased' individuals. There's no eliminating the human factor, and the desire to do so seems to me futile and misconceived.
"...every mind has a new compass, a new north, a new direction of its own, differencing its genius and aim from every other mind; as every man, with whatever family resemblances, has a new countenance, new manner, new voice, new thoughts, and new character. Whilst he shares with all mankind the gift of reason, and the moral sentiment, there is a teaching for him from within, which is leading him in a new path, and, the more it is trusted, separates and signalizes him, while it makes him more important and necessary to society. We call this specialty the bias of each individual. And none of us will ever accomplish anything excellent or commanding except when he listens to this whisper which is heard by him alone. ...A point of education that I can never too much insist upon is this tenet, that every individual man has a bias which he must obey, and that it is only as he feels and obeys this that he rightly develops and attains his legitimate power in the world. It is his magnetic needle, which points always in one direction to his proper path, with more or less variation from any other man’s. He is never happy nor strong until he finds it, keeps it; learns to be at home with himself; learns to watch the delicate hints and insights that come to him, and to have the entire assurance of his own mind. And in this self-respect, or hearkening to the privatest oracle, he consults his ease, I may say, or need never be at a loss. In morals this is conscience; in intellect, genius; in practice, talent; not to imitate or surpass a particular man in his way, but to bring out your own new way; to each his own method, style, wit, eloquence." - Emerson, Greatness