For example, if their is an unrated player without a boarder or a player that is Silver it's like painting a target right on their heads for blame. It's sad really. In other cases I'll find that Diamond or Platinum players will berate the gameplay of everyone else that isn't the same rating as them.
In my last game a guy went mid Lee Sin and was apparently platinum, a person in the champion select said "watching too many streams eh?" the guy playing Lee Sin responded with "i dont need to hear from a silver" after the game had loaded.
Another example is it causes a demoralizing effect for some "oh great 2 unrated players gg" sort of thing. There needs to be an option to either toggle your boarder on and off or toggle the ability to see other boarders.
TL;DR It's causing a segregation of sorts depending on how high up you are. It's causing just plain bad attitudes towards others before anything even happens.