Yes, you are. That's literally your role and reason for being in the party.
Flip it to any other class and some of their assumed roles in the party.
"So in your opinion if I play a fighter I'm required to protect the squishy characters in the group without fail or question?"
Yes, you are.
"So in your opinion if I play a magic-user I'm required to let everyone else sleep in my Leomund's Tiny Hut without fail or question?"
Yep.
"So in your opinion if I play a thief I'm required to scout ahead, search for and disarm traps, and search for secret doors without fail or question?"
Yeah.
"So in your opinion if I play a ranger I'm required to share my foraged food with the rest of the party without fail or question?"
Still yes.
Now, a really relevant question. Why? Why should the strong fighter defend the weak wizard? Because the wizard will help the fighter in the future. Why should the smart wizard help the stupid thief? Because the thief will help the fighter in the future. Why should the nimble thief help the clumsy fighter avoid the trap? Because the fighter will help the thief in the future. It's called teamwork. If you're not playing a team-oriented character, you've failed to make an appropriate character for the default assumed playstyle of D&D. A group of individuals on a team to provide mutual aid and support so that they can collectively overcome obstacles that none of them could face individually.
I view non-cooperative characters in the same light as non-adventurous characters. You wasted your time making a character that won't actually fit with the group. Cool. You want to lone wolf it in the corner? Sure, the rest of us are going on an adventure? Wanna come? Then be a team player. "But it's what my character would do?" Okay. Our characters would leave your butt at the bar and go on without you. We can hire a cleric, thief, fighter, wizard, or whatever else to replace the selfish character you made that we left behind. We're under no obligation to drag you along and let you be disruptive to the rest of the group. D&D is a collaborative activity. Making a selfish character that would withhold their contribution to the team is to decide to not be collaborative with the group. Cool. You're out. Hope your replacement doesn't pull the same BS otherwise they'll be out on their butt too.