One of the small paradoxes of aging is that older people are on balance more satisfied with this business of being alive, despite suffering a growing burden of the consequences of degeneration. A related paradox is that most people, if asked, will say that they want to age, decline, and die on the same schedule as their parents and grandparents. It is possibly the case that we humans are just not very good at the important things, the ideas and decisions that really matter. Conformity is more important than life. We readily sabotage the person that we will be a decade from now. Progress happens by accident, and we collectively random walk towards an incrementally better world because we are collectively incapable of taking the logical, direct path - whether that is towards an end to violence, an end to suffering, or an end to aging.
Ask people if they would like to live longer, perhaps even much longer, so that they could have more time. Initially, they'll say that the problem is quality, not quantity. Once you've convinced them to focus only on the benefits, you're bound to still face some skepticism. Nearly everyone grew up in a cultural context in which the fact that human life is limited is depicted as a blessing in disguise. There really isn't any proof, or even convincing evidence, that living longer than we do now would wind up being demotivating or boring, yet it's something that people commonly believe.
As avid a lover of life as I am, there are dull moments, moments that I'd rather forget, moments that don't count at all, and moments at which I'd rather lie down and slack off than "live to the fullest". I am okay with that, because life is made of ups and downs. We've got needs that periodically require taking care of. That's why you don't want a party to last forever; after a while, you need quiet and privacy. Later on, you'll feel more social again. This is the point at which people are likely to draw a false analogy and say that life is just like that party: at some point, you'll want to leave.
Life should be enjoyed. This doesn't mean that you should expect to be hyped all the time, but if you have a choice between enjoying any given moment and hating it fiercely, why not the former? If you can maximize your own enjoyment without harming anyone, why not? That's something to think about in general and something that people who are skeptical about life extension should ask themselves. Being sick hardly helps you enjoy yourself; so, if you want to maximize your enjoyment, you want to stay disease-free as much as possible. This is the point at which people need to understand that elimination of disease and life extension are one and the same: you can't really have one without the other.
As life extension technologies would likely allow us to live much longer, they would allow us to maximize our enjoyment by maximizing its duration; of course, this is only a possibility, as your enjoyment of your extra time depends very much on what you do with it. This is the point at which another objection is likely to be brought up: Are the extra years granted by life extension going to be more of the same old stuff? I don't have the foggiest clue, because it depends upon a number of unknown factors, one of which is you. If you're afraid that you'll spend your additional years doing the same old boring job, I'd say that you've got a problem with your job, not with life extension.