i feel that, within reason, yes, agressive play should be allowed. i define reason on a similar plane as FIRST, blocking/pushing/and otherwise forcing your opponent should only be allowed for a few seconds at a time before penalties should be enforced. For obvious reasons, full speed ramming (like what happened in Koko Ed's video) is dangerous, not gracious or professional in any way, and should not be allowed.
But whether you run your robot into a concrete pillar in st. louis while programming *on accident!*, or anticipate getting hit around a bit by the competition, a steel frame is always a safe choice
...by the way, we did more damage to that pillar (a few small chunks flew off

) than we did to our robot (nothing)