Defensive robots have their place on most alliances. Team
179 Children of the Swamp played some extreme defense in 2007 and were finalists on Einstein. Most robots play defense like 179 and just push, push, push but some use other strategies. A few this year made their robot as big as they could and tried to block robots shooting from the key. Previous years included robots that kept game pieces away.
We design our robots to have a minor in defense meaning that if our offense fails we can still play effective defense. 6wd traction wheels with AM supershifters give us a good edge when competition comes around and we have no trouble pushing people around and pair well with our offensive strategies because we can normally out maneuver a defender.
You are right every robot should aim to be offensive but in an equal way every robot should have a last ditch play aka defense.