Yes, ofcourse there would have been more guilt and it would have been something really unforgivable.
Because all the arguments we are giving in Viaan's favour are because we know Viaan is not actually a bad person and his past experiences played an important role while making that proposal. But we can't say any of those things if there would have been any other person. May be that person wouldn't even have considered katha's consent once she arrived in the room.
And when one has to test someone based on their experience then they must do it themselves, they cant share the burden and responsibility by involving third person to it.