Physics at e^- e^-: a Case for Multi-channel Studies

I argue that it would be crucial to have as many channels as possible to understand the physics of electroweak symmetry breaking (EWSB) in next-generation collider experiments. A historic example of the parity violation and the $V-A$ interaction is used to make this point. An e^- e^- option offers us a new channel in this respect. The usefulness of this channel is exemplified for the case of supersymmetry and of the strongly coupled EWSB sector.