re: Person in my league gets Dez Bryant for Darren Sproles...

The veto option isn't there ONLY to prevent collusion. Then it would be called an anti-collusion-vote. You get the option to veto trades that are unfair to the rest of the league.

I've seen people on here say "you cant veto if someone is stupid and the other one takes advantage of it" or "only veto if its obvious collusion."

No, i disagree. You can veto for a myriad of reasons, and in this case: one team is getting WAY stacked while the other gets no real benefit other than RB depth. Did you see the part where two of his STARTING three receivers will be Mike Thomas and Malcom Floyd?

It's unfair. Therefore, a veto should be allowed.