I think we've gotten too hung up on a specific word, but if you really want to bring the dictionary into this, are you saying you owe it to other people to give them as many possibilities to decide for themselves? I would have to disagree with that assertion.
Think about it in reverse. Suppose your boss is thinking of increasing your responsibilities along with a significant pay bump, but they think about it and make the assumption that you like your current role and wouldn't like any new responsibilities. Wouldn't you rather make that decision yourself?
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?
Yes, I would like to make those decisions. No, I don't think I'm owed the right to make them. To say otherwise would be silly; if we all honored such a right we'd be forever trapped navigating an interminable labyrinth of negotiation and consensus-reaching.
reaching consensus and building unity is a good way to strengthen a community, organization or team, so no i don't think we'd be trapped. on the contrary, everyone would feel empowered.
most of our problems today are coming from the fact that people are disempowered and lack the agency to improve the situation.
you need to seek consensus, in order to reach it, so i disagree. of course, if you can't find consensus after sufficient negotiation then that is a problem, but it depends on the nature of the relationship and the nature of the point in question, how much of a problem it is.
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.
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"