No, I am not 'deciding it', I am judging it. And you can judge it too.
So, take Superman and Clark Kent. They're one and the same person. Consequently, anywhere Superman is, Clark Kent is, and vice versa. Given that they're one and the same person it is obviously impossible for Superman to be somewhere and Clark Kent not.
Now, imagine someone denies this. I would not 'decide' that the person in question was a total idiot. Rather, I would judge that they were. As, surely, would you - yes? I mean, something has either gone seriously wrong with their ability to reason, or they just don't grasp concepts like 'one and the same'.
If you agree - if you agree that in the above case I would not just be dismissing the critic, but justly deeming them an idiot and their criticism misguided - then consider identical argument.
If being morally valuable and being valued by me are one and the same property, then if I value something it must be morally valuable. Forget the fact they're obviously not the same property - that would be like getting hung up on the fact Superman doesn't actually exist. 'If' they are one and the same property, then obviously anything I value will be morally valuable - why? Because - by hypothesis - that's just what being morally valuable involves. Nothing more, nothing less.
So, now consider this premise:
1. If being morally valuable and being valued by me are one and the same, then if I value something necessarily it is morally valuable.
That's obviously true. Someone who didn't see that it was true is literally as idiotic as someone who doesn't see that this is true:
1. if Superman and Clark Kent are one and the same person, then if Superman is in Texas, necessarily Clark Kent is in Texas.
Yet if you go through the thread above you will find several people - one in our immediate vicinity - denying that this premise is true. And these people have the cheek to represent themselves as knowledgeable about logic and keep telling me I don't know enough of it.
Just consult your own reason though and tell me if you agree with me, or with them. Do you agree with me that if I am the pope, then if the pope is in a brothel I am in a brothel? Or do you agree with them and think that if I am the pope then if the pope is in a brothel I might not be?
Am I just 'deciding' that they are mistaken? Or am I entirely reasonably judging that they are mistaken?
Or take this argument:
1. If P, then Q
2. Not Q
3 Therefore not P.
is that valid or invalid? Well, it is obviously valid. Someone who kept insisting that it was invalid is just a berk, plain and simple. And yet there are many above who have denied that my argument is valid despite it having precisely that form.
Am I just 'deciding' that they are wrong? Doesn't your reason confirm that the above argument is valid?