Does it really matter if it takes a century to materialize?
Yes, it really does matter. If it's a century off, we'll probably manage it all wrong if we try to manage it now. The longer we can wait to deal with the problem, the more prosperous we'll be when we deal with it and the better the technology we'll have to address it with. Also, the more science we'll know, so our chances of screwing it up will be lower. (Imagine if we invested tens of billions into electric cars and trillions into nuclear power in the 70s because we were told we only had 20 years of oil left.)
You're not really that egocentric that you're willing to screw your children and grandchildren for the comfort of driving a SUV today, are you?
The difference between this simplistic silliness and reality is why this kind of reasoning is complete nonsense. It's not about driving SUVs, it's about growing global economies so that we have the resources and understanding to deal with big problems the best way possible.
Every reduction in human population is one less ticket in the lottery for the next Einstein or Beethoven. The stakes are as high as they can be.