This is something I struggle with too.
Like, if a theologian is totally off the rails in one aspect, why would I read her (or his) other books? And yet, there are some theologians that are *fabulous* in one (or more) areas, despite their complete lunacy on some tangent.
My pastor is really challenging me to move beyond the "why bother" mindset because it really does cut me off from some amazing books. It's just a question of having a well-calibrated hooey-meter that can flag the scary stuff. And that takes practice too, especially in a new field.
Hence why we're meant to live/learn/work mostly in community, probably, so that I can say, "Hey, what do you think about this?" and get feedback from others.