I feel I have to defend the "I don't mind" crowd a bit, because I remember some childhood experiences: it might be that some people were rarely allowed to make decisions while growing up, they always had to go with the flow to keep the peace, perhaps if they had a lot of brothers or sisters.
I much prefer the answer "I don't mind" to the one which is far worse:
"Dunno." Or "s'pose so" to something suggested.
Perhaps some of the "I don't mind" crowd had authoritarian parents who decided everything, and never involved children in their decisions. They might have been told "the only choice is: take it or leave it". Or they might have had parents who frequently gave them commands disguised as choices (as advocated by MN), such as "come on, it's bedtime now. Do you want the Peppa Pig or the Elsa nightie?". An insignificant choice to sweeten the real message, I remember seeing through that. If my mum offered me a choice, sometimes it wasn't really a choice:
Mum: Would you like strawberry or chocolate?
Me: Chocolate.
Mum: Would you mind having strawberry, because it's already open?
Why offer me the "choice" then?
Also "are you going to put your things away?" Or "you can either stand in the corner for twenty minutes, or you can have a smack, and it's all over quickly." What difficult choices.
When I was a driving instructor, I met some teenagers who were so indecisive, it was as if they had never made a decision in their lives, everything had been planned for them. They wouldn't have chosen to have driving lessons, they were given as a birthday present. This seemed to happen more with the wealthier ones. "You're going to Eton whether you like it or not, this is what you will study at university because your Father did, etc."