I think I understand why they did it, too. They valued their position, their trappings, their status, above what was actually being disseminated to the people. When somebody came and said, "hey, I think we've misunderstood, and here's why", they didn't respond with an open mind towards the scripture. They responded with fear of losing what they had, regardless of scripture and fact.
I'm not sure why you are assuming the worst of everyone involved. Would you also say that the close-mindedness of Jonah in the OT, and Peter in the NT, negated the authority of the words that they did speak on behalf of God? Personal failings have no bearing on the office which, I believe, God established to convey that which He wanted us to know.
There is no question in my mind that there have been some who have behaved atrociously, and there is no defense of those individuals. However, I count <5 rogue popes out of 264+/-, which is a better ratio than the apostles themselves. Does all that Jesus said get thrown out because of the betrayal of Judas, the denial of Peter, the persecutions of Saul/Paul?
You don't believe in the Catholic Church, and that's fine with me. But, as a Christian (which I'm assuming you are) you should try not to judge the intentions/hearts of any people, especially those who's lives you have merely a snapshot.