And they absolutely turn people off. The thing is, as long as it doesn't turn everyone off, it allows the project to move forward, because even with burned bridges, it leaves ownership clear.
Communal decision making, however, does not have that advantage. If both sides of an issue, so to speak, become turned off of one another, you are more likely to have an abandoned project. There are, of course, other advantages (you don't miss generally accepted "good ideas" because of the particular vision of one person, and you can apply community standards to everyone, rather than having to weigh "continued participation in this project that is important to you" vs "dealing with -that- asshole again"), but that is definitely one con.