This is where the idea of rating the leader comes in. You only get to rate positively; an "I liked being in a group with this person leading" button, don't even have a ratings scale, you either liked them or you didn't; in the situation you just gave the people in your group would not be able to do anything except not rate you. (If you were not the leader of the group they wouldn't even have the option to rate you positively since it would be leader rating only.) The problem with this comes new players; new players will have a lower rating or a non existent one, and will have a hard time getting the chance to even prove themselves. A potential fix would to put a 3 month "This person is new" icon in place of their ratings while the ratings get built up. The problem with this is players waiting a while before leading anything, players that don't lead groups for a long time and then later decide they would like to, players that re-activate their accounts after a hiatus. Though these people again could have an icon "recently re-activated" to give them a chance to build a rating.
Other options; if the ratings are done divided over time this has potential problems if you start grouping with the same people over and over again if you only get to rate one person once. If you get to rate multiple times, then guilds could rate their players up highly even if they are not good leaders.
So yes, many potential problems with a rating system, but if it is the only way for Blizzard to give us back the ability to create our own groups without a lot of fear from the community then I think it is a necessary evil. After a while things would settle down, people would have made friends with people online at the same time as them, and would have found a group of people to run with each day; a new untested leader no longer becomes an issue.
May I ask how long you have been playing? Just so I can get an idea of which features and group types you have experienced in your time here.