This seems abstracted enough to make it impossible to answer, as it depends on the nature of your relationship, the action, and the harm. E.g. if you are risking direct bodily injury to P, then he would have much more of a right to veto it than if your action was something like “I will carry out research into a controversial topic which might end up upsetting other people and make them angry at me, and also angry at P by association since we are known to be friends”.
But in general, would you want someone else to unilaterally carry out an action that you felt had a high risk of harming you, just because you failed to convince them of this being the case?
This seems abstracted enough to make it impossible to answer, as it depends on the nature of your relationship, the action, and the harm. E.g. if you are risking direct bodily injury to P, then he would have much more of a right to veto it than if your action was something like “I will carry out research into a controversial topic which might end up upsetting other people and make them angry at me, and also angry at P by association since we are known to be friends”.
But in general, would you want someone else to unilaterally carry out an action that you felt had a high risk of harming you, just because you failed to convince them of this being the case?