If you and your friends were trying to decide what to do next weekend, would you give a vote to the friend who was going to be out of town that weekend? People should not have a say in matters they won't be around for. I'm not allowed to vote in Canada, nor should I be, because I don't live there. Similarly if I am near death, I should not be allowed to cast a vote on matters pertaining to the future because I won't be there.
It's also worth noting that short-vs-long-term planning is just a paradigm for thinking about your politics; in practice, absolutely horrible things can arise from both strategies. Long-term thinking can manifest as clinging to tradition (since you now feel ownership over future generations and want to impose your own world-views on them). It can manifest as early optimization. Both of these things can be good (maintaining culinary/aesthetic culture, infrastructure investment) or bad (maintaining brutal and oppressive traditions, prematurely and hence inefficiently optimizing things at tremendous economic/social cost).
I'm not saying the status quo is anywhere near optimal. I think it's a very interesting (read: hard) and probably culturally-dependent question of what age groups are able to minimize the societal happiness cost function (and of what that cost function even is). It's incredibly difficult to say anything generally meaningful about how you might do this well. The one-person-one-vote system is at least a simple solution that seems acceptable to most, which is an important feature (not that each person's vote counts the same in practice in USA, but that's a whole other problem).
We don't let teenagers vote because they're known for being hotheads, but when an 90 year old man forgets the names of his children, we still let him vote. That's nuts, and it shows that what we have right now is not a 1-person-1-vote system. We already have a system of selective enfranchisement, but it's not been configured in a rational way. It's not been configured in a way designed to give good results. In fact, it's proven itself quite harmful. Go ask any climate scientist what our future on this current trajectory looks like. Trying to stay the course is suicide.
How does that show any such thing? Unless you're defining someone with dementia as "not a person".
> Go ask any climate scientist what our future on this current trajectory looks like. Trying to stay the course is suicide.
Ah. You're against old people voting because they don't vote the way you want on your hot-button issue. And you're willing to sacrifice the right to vote on the altar of climate change. No thanks. (But it makes me wonder what else you're willing to sacrifice there...)
Are 17 year old people "not persons"? Of course not. Who is talking about non-personhood?
We currently forbid 17 year olds from voting (while allowing them to sign up for the military..) but where are the objections when a 75 year old with dementia and the mentality of a 5 year old votes? The 17 year old is unquestionably more qualified to vote than a senile pensioner who thinks Jimmy Carter is still in office and forgets to walk to the bathroom when nature calls. That's the case even if you disregard the "skin in the game" argument, or even if you somehow convince yourself that democracy is more important than bracing humanity for catastrophic climate change.
But if you want old people disqualified because you don't like the way they vote, get lost.
Or would it be better to have some of those people, as voters, to be able to say "wait a minute" to some stuff that sounds good to people who haven't been through similar things?
It's almost like black and white statements are just bad stereotypes.
Are they malicious? Maybe, maybe not. But at the end of the day it doesn't matter if they're malicious, senile, or just plain old apathetic.
(Perhaps you can find a political issue for which young people throw caution to the wind and old people exercise appropriate caution, but I can guarantee you that the impact of that issue will not be as severe as climate change.)
And you don't like it when the other side does it...
A revolution could well not go the way you want, and end up in a system where no one can even defend fighting climate change, or worse, everyone has to enthusiastically pretend we're doing a heroic effort that is well on track to solve the problem.
On the other hand, someone over 70 might be more likely to vote for the general good rather than their selfish interests.
Evolutionarilly speaking, the reason humans have old people at all is that they contribute wisdom. Otherwise, people would tend to die soon after their children reach adulthood. There's no incentive for evolution to favor useless organisms that aren't able to reproduce - so old people aren't useless.