just to clarify, since there are a lot of "you"s and "opponent"s used in the description
player A has a unit with sadistic mutation
player A attacks player B with that unit with sadistic mutation
Sadistic mutation says "Forced: After the attached unit deals damage in combat, deal 1 damage to one target unit or capital."
so player A gets to deal 1 damage to player B's capital, and player A gets to choose the section that is damaged?
and this works the same way with any card that says "target a capital" unless the card specifically says the owner gets to distribute the damage.
lesson to be learned. No matter how emphatically any particular "player" on this forum states their belief in a specific interpretation, unless they have an definitive email ruling from a game "designer" or the rulebook/cards, DONT PASSIVELY AGREE WITH THEM if it goes against what you feel.
additionally, just cuz you feel strongly about an interpretation, have the wisdom to realize when there are "reasonable" ways to interpret the situation differently, and be open to the logical reasoning that other people present.
oh yeah, and whenever you start feeling the urge to post a snarky message on the forum., maybe its time to actually send the question to Nate
(Gloriuly killing my own units and then let my rangers burn down the opponents zone(s))