Aristeia

Yes we often do give nage our ukemi - i.e. we make a concious decision to roll. Not always, I like another poster did my first top ukemi of a kotegaeshi with no idea that it was about to happen. But many times we make a decision to do an ukemi.

The best response I've ever heard to that is that taking ukemi is like tapping out in grappling arts.
People don't tap out in real life, just like they don't do big ukemi in real life. The ukemi is a signal that yes you have compromised my balance to the point where I'm in danger of injury so I must abandon my attack and protect myself. And just like tapping out, if you choose not to take ukemi, then bad things could happen to you. It won't necessarily look pretty like in the dojo, but it will stop the attack.