Either way, their capacity to act (agency) remains intact.
The very important phrasing, in my estimation, can lead people to neurotically question their feelings less they "rob" someone of the capacity to act. In reality, a more lax quip such as "assuming makes an ass out of u-&-me" gives people more breathing room for their lapses in judgement.
to deprive of something due, expected, or desired
So to say you're "robbing someone of their agency" is the same as saying you're "depriving them of an opportunity to decide for themselves"
Or suppose you're single and there's an attractive acquaintance who is thinking of asking you on a date, but they overhear you talking to a friend about a date you had, and so they assume you wouldn't be interested. You don't want to make that decision yourself?
most of our problems today are coming from the fact that people are disempowered and lack the agency to improve the situation.
failure to reach consensus could threaten your relationship.
if my boss keeps making decisions for me then i'll eventually quit my job, because i am not willing to work like that. and if my partner does it then it will lead to a breakup and if it is something else, a judge might force a consensus on us.
"He's always talked about working more with his hands, I probably shouldn't forward him this desk job that'd otherwise be perfect for his career progression."
"She'd never date a loser like me."