The catalytic converter was an add on that scrubbed exhaust. In my opinion there is a big difference between adding a filter to emissions and forcing manufactures with so much regulation that they have to produce a certain type of vehicle. Remember the Pinto and Chevette? I'm not against raising CAFE standards, I'm against over intrusive government and the idea of taxing older cars out of existence.
If Honda figures out how to make 7 passenger carbon fiber minivan that gets 35MPG and leases for 299$ per/month I'm all for it but that's not going to happen any time soon.