Ah... I remember 2003 when tipping was not so heavily penalized. My team's robot had parked sideways on the top of the ramp, and a certain team (will not mention their name, they are good friends actually

) lowered their manipulator like a battering ram and slammed into us at full speed, not only knocking us off the ramp, but tipping us, AND get this, snapping two of our skyway wheels because they got caught in the mesh of the ramp as our bot tipped over. Good thing we had spares.
As for how I felt, I was only ticked off because the wheels snapped and we lost the round. I personally do not think that team did anything that was not graciously professional. Sure our robot got messed up, but they won the round by knocking us off.
I think that if a robot is already on top of the ramp, and another robot gets up on the ramp and pushed the first robot off, and tips them over in the process, it may deserve a penalty but it is not anti-GP. It is strategy.
And to the original point, a robot that tips a robot as it is trying to get onto the ramp should be dq'd. If you want to prevent them from getting up on the ramp, just park your robot. If they tip themselves on your robot without yours moving at all, too bad for them.
It is all just how you apply your robots power. If it is to remove a robot from the ramp, push them hard. If it is to keep a robot off, you dont need power for that, so there is no excuse if you tip them over.
I guess the end point is, tipping is sometimes an evil thing to do, but it is also just sometimes happens. And I have seen teams that have had their robot tipped be more anti-GP then the team that tipped them, simply by, Im serious, screaming profanity at them. So remember, treat other robots as you would like them to treat your robot. It keeps everyone happy, and prevents screamed profanities.