These days a lot is made of defense tackling with no arms - ie shoulder charging the offensive player or simply running into him. But why is it not an offence if the attacking player simply turns his shoulder into the defender?
Also a hand off in the face is a valid attacking tactic but if a defender pushed his hand into the attackers face then he would be penalised.
Why the disparity? For me the attacker should not be allowed to run shoulder first into a defender as he is likely to injure him.
The difference is that a tackle is an offensive move and the law states how it should be done safely. The tackler is driving into the ball carrier, the momentum is with him. The ball carrier is merely defending himself and has no energy or momentum going into the collision. It's all about safety.
The Rugby Ref