The post here by Genevieve Maitland Hudson is marred by a piece of fashionable guardianista silliness suggesting that Tony Blair might have thought his own sincerity was sufficient grounds for going to war in Iraq (on which type of thing I've pretty well said what I want to say already). But I commend the post to you anyway. It contains some sound advice.
There's a school of thought according to which, if you have 'issues' with people you know reasonably well, the best policy is to be upfront about it. Just say what's on your mind, talk things through in an open way. My own experience, for what it's worth, is that this can easily bring on disaster. There are people between whom it can work, done with care and mutual consideration - some family, some intimate others. But with those at a greater emotional remove, and even with some friends, directness often burns too hot. Better stick to conventional forms of politeness: to tact, discretion, not saying what you think.