I regularly practice aikido waza in pubs with my inebriated friends. Some of them are regular aikido practioners, some practice other martial arts, and some know very little at all about martial arts.
Obviously, we don't take ukemi in the pub (although there's one crazy Italian guy I know who loves to show off and take breakfalls on the dance floor
So of course, you can show people of all levels stuff without ukemi, but it certainly isn't serious practice -- it's more like part of a conversation. You're just showing somebody something as an example. You're giving them a "taste" of aikido.
If somebody really wants to learn aikido, they've got to take falls. After all, ukemi is also self-defense.
Ukemi is also an important part of the total experience -- the sharing and trusting of our entire being for the purposes of training. It's the most beautiful part of aikido -- one of the things that make the art somewhat unique. It teaches us to be unselfish.
Ultimately, in aikido, we're learning to work our hara in such a way that it moves another's hara and brings their energy back into harmony, which somtimes ends in a throw. This is how we train.
Actually, if you think about it, throwing is useless for fighting -- the guy could just get back up and attack again. We use throwing in aikido as a training tool to learn to work our hara properly.