Barbarians don't actually attack their allies or anything like that in 5e.
True, but “raging” in 5th still has a bit of that element of losing one’s self within the anger. It is a source of physical strength, coupled with profound limitations. JM’s anger doesn’t really make him stronger, it doesn’t render him incapable of using the skills, knowledge & tricks he has at his disposal. He’s resourceful, not “primal”.
Rage
In battle, you fight with primal ferocity. On Your Turn, you can enter a rage as a Bonus Action.
While raging, you gain the following benefits if you aren't wearing heavy armor:
• You have advantage on Strength Checks and Strength saving throws.
• When you make a melee weapon Attack using Strength, you gain a +2 bonus to the damage roll. This bonus increases as you level.
• You have Resistance to bludgeoning, piercing, and slashing damage.
If you are able to cast Spells, you can't cast them or concentrate on them while raging.
Your rage lasts for 1 minute. It ends early if you are knocked Unconscious or if Your Turn ends and you haven't attacked a hostile creature since your last turn or taken damage since then. You can also end your rage on Your Turn as a Bonus Action.
Once you have raged the maximum number of times for your barbarian level, you must finish a Long Rest before you can rage again. You may rage 2 times at 1st level, 3 at 3rd, 4 at 6th, 5 at 12th, and 6 at 17th.