to the guy who compared baseball to football -- there is no comparison. Football trades are a different animal, as everyone can be reduced to a point total far easier than in roto baseball. The draft is much more important.
In baseball, trades don't ruin leagues at all. They CAN ruin leagues, which is markedly different. Trading is practically necessary (as opposed to football) because you NEED points in every category, and you can't always get them through the draft. Trading in roto is also different because of the finite amount of points to go around. In a good league, trading ups the fun level, not detracts from it, because it can become like a chess match. Your gain is by definition someone's loss in roto -- so I think that complaint falls on deaf ears.
As for trades and their values -- I know what they guy is getting at:
These players are (for the most part) on my roster for a reason. I obviously valued them higher than the rest of the league, or I would have passed on them and picked someone else.
The rule isn't absoloute of course.
But I get VERY irritated when I get trades soon after the draft that don't account for my draft position. Unless it fills a need that I got screwed on later, why bother? You can obviously tell that I prefered one player to another through the draft board. I got offered beltran for pujols this year, not half and hour after a draft. Come on, if I wanted beltran, I would have just picked him (I had the number one pick).
As we move away from the draft, obviously this dilutes.
One other thing: People, in the course of overvaluing their players also have blinders on to needs, and tend to resent being told "what they need." I think there is a balance to be struck honestly. Send your offer, if they reject, send it again later (keep a email folder for this). If it is fair, maybe they realized their error and are more amenable to it. It is especially true with pitching now, as teams are relaying on a lot of arms that should revert to the mean sometime soon.