They proclaimed to know the way to life, they made people think that their way is the way to discovering true life. They had the 'keys' to kingdom, but wouldnt let anybody else enter. They were stumbling blocks to those who desired freedom. What they proved to be to the people, were death. Which is why Jesus compared them to whitewashed tombs. Nice on the outside, but full of dead mans bones on the inside. Their theories and theology was based on the living words of god, which should prove to bring life to people, accept when they used it, they brought death.
His gripe with them was that they were not the 'life' they proclaimed to be.
Ever been in the presence of someone for ten minutes and you felt like you need a holiday? These people suck the life out of you. They are hypocrites.