Why does that make it unfair?

The diagram has omissions. Either:

1. There is a floor that the weights (and the man) are standing on.

2. Weight C is dropping whether he pulls the rope or not.

I think that the diagram is meant to show all the weights resting on a floor, and all the confusion is due to misunderstanding of that. In the other case, the diagram neglects to mention something to the effect of "supports have just been removed".

Is the person currently pulling, are the weights on the ground, are the weigths currently moving to get into a stable position? Friction, weight of cord, acceleration, etc. etc. Any combination of the previous?

Depending on your level with maths/physics you'll probably give different answers and make different assumptions.

In physics problems things are assumed idealized unless they aren't. Also, velocity doesn't matter here, and no math is required to solve the problem.

I didn't know physics problems are assumed to be idealized... When you build a bridge for example, will the physics try to be simplified to the max? (Honest question here).

Velocity would matter -- it seems to me -- if there is friction and probably a few other factors included like elasticity. No?

Personally, I always considered physicists to be applied mathematicians (not the other way around although I've seen physics problems thrown in university level math classes). That's why I put that there, so assuming a high level of math skills, you'd probably change your way of thinking quite a bit.

When you build a bridge, that's engineering, not physics. It's a physics convention that unspecified factors are assumed to be unimportant. If they were important, they would be specified.

Anyway, it's implausible that the elasticity of the rope or the friction of the pulleys are going to matter. Unless you have really rusty pulleys, or something.