Unitarian Universalism is about the least objectionable religion imaginable. They don't go door to door trying to convert people. They don't try to prevent gays from marrying. They don't try to get creationism taught in schools. They don't say that if you don't believe as they do then you'll burn in hell.
But there's one major problem with UU that I find objectionable. They're too open and accepting.
The thing is, the existence of god and other religious questions are objective facts. Either god exists, or god doesn't exist. God can't exist for you, and not exist for me. If one person believes in god, and another doesn't then one of them is wrong and ought to change their mind, because truth is important.
Now, I don't think that someone with wrong beliefs should be censored or converted at swordpoint or anything like that. The only way to separate the true beliefs from the false is to constantly examine and challenge all beliefs.
But if a congregation is truly interested in getting at the truth, they shouldn't be content with "Well, some of us believe in god X and some of us believe in god Y and some of us don't believe in god at all.". They should instead examine the evidence and try to determine which, if any, beliefs are true and believe in those. Eventually, as they share information and arguments, they should start to agree on major points.
UUists tend to like the parable of the blind men and the elephant. They use it as an example of how different people can experience the same reality differently. But the parable shouldn't end with one man feeling a rope, and one man feeling a wall and one man feeling a pillar. Rather the blind men should examine the elephant further, switch places and find parts they hadn't before, and hopefully find a unified elephant.