Stupidity: Major Franklin is struggling up the side of the cliff while the rest of the group are on top of the cliff checking their equipment, then he slips and slides down the cliff side, breaking his leg. After seeing this, the group members reach for a long length of rope that was used to bring up the other members and the supplies. The commandos could have used the rope to help Major Franklin climb up and prevent him from falling and injuring himself.
Stupidity: When Mallory decides to answer the phone on the cliff top he's warned there will be a code word or phrase. It seems to me that a better choice would be to not answer. Even though there would still be a patrol sent, isn't it more likely that a sentry had accidentally fallen off the cliff than unknown commandos climbing such a challenging face in such horrible weather?
Stupidity: Since the resistance fighters were already on the island, they could have just lowered a rope from the top of the cliff and "top roped" everyone up. No special climbing skills would then have been required.