Is duncan a fool for going to macbeth's castle and not suspecting the danger posed to him there by macbeth and lady macbeth why or why not?

Is Duncan a fool? No.

Reasons Why: 
Reason one: Duncan isn’t a fool for going to his house but a fool for not having protection while he rested. Reason two: Duncan isn’t a fool for simply trusting a man that helped win a war. Reason three: Duncan isn’t a fool because he didn’t know Macbeth was plotting to kill him. He was blinded because he thought Macbeth was a good Samaritan. Conclude:

Duncan wasn’t a fool but he was foolish to trust a fool that plotted to kill him and succeed. Duncan wasn’t and still isn’t a fool because he trusted a simile and mustache. Duncan trusted the wrong man that did good deed but the lesson learned here is that a person can do well just as much as a person can do wrong and that greed is the ultimate seed to.