None of my attendings are idiots. I might have called a few of them idiots while ranting over dinner with my coresidents/cofellows, but all of them are all board certified in my field and got through training, then were hired by my program.
Some may have different practice habits than the most recent sets of guidelines. Or based on their clinical experience. Occasionally, this is because they are not aware of the most recent evidence. Other times, it is because they have reviewed the underlying papers behind those recommendations and disagree with the interpretation. And other times, it's because they simply have their own way they like to do things, evidence be damned.
When I run into this situation, I try to discuss the plans with them to learn which situation we're in. Lets say I still disagree with the plan but it is something that is minimally harmful to the patient (obtain more labs, or whatever), I'll drop it and move on. If I think it's something harmful to the patient, I'll typically push. If we have time, I might pull the guidelines, ask the attending to discuss, and often I can get them to change their minds (or convince me they're right). If they insist on their way, then I make a note of it, do what they say (given it's their license on the line since their name is at the bottom of the note), look up the evidence for myself later on, and just understand I won't manage it that way when I'm in independent practice.
You have to understand, most of the stuff we do doesn't really matter that much. There's a lot of ways to skin a cat, and even treating a patient in a less than ideal way usually won't lead to long-term negatives. I've never had it where the attending is insisting on something definitely acutely harmful to the patient, but if I did I'd probably push harder.