I hope that, in the backlash against roles, we do not forget the problem that roles were developed to solve: anemic classes that didn't do anything well. (Now, whether or not you, personally, saw that as a problem is a separate issue, but there were a number of complaints made about classes such as the bard and the monk).
At the most basic, having a role meant that you had the mechanical backing to do at least one thing well,
if you chose to do so (this latter part is often de-emphasized when roles are painted as limiting or pigeon-holing):
If you were a defender, you had a mark mechanic. (Mind you, since some people don't like mark mechanics, this further taints the concept of roles for them.)
If you were a leader, you had a healing mechanic. (And if they also disliked 4e-style healing, it's possible that some of the dislike spread to the concept of roles, too.)
If you were a striker, you had some extra damage mechanic.
If you were a controller, you (usually) had an at-will attack that affected multiple targets.
The other point about roles that tends to be de-emphasized is that they don't actually constrain the characters very much, since every class has powers that blur the roles, and multiclassing makes individual characters even more flexible. In addition, the lack of a mechanical advantage shouldn't prevent you from doing things, any more than being untrained in Stealth prevents you from hiding, or being untrained at Perception means you can't notice things. If you're not a striker, you can still deal out damage. If you aren't a defender, you can still get between an enemy and a badly wounded ally, and be no worse off than any character in any edition who doesn't have a mechanic to make the enemy want to attack you instead of your ally.
That said, roles can create a
psychological constraint on player behavior. In much the same way that having a list of powers focuses attention on the list and can discourage some people from attempting things outside of it, assigning roles to classes and characters can focus attention on the role, and discourage some players from attempting actions that seem to fall outside the role.
IMO, explicit roles aren't going to be in 5e. However, I'm sure that they will be there in the background, helping the designers to ensure that there will be no anemic classes in 5e. Which is perfectly fine, in my book.
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