It's a good argument, however I think it's pretty clear to a lot of people that today's issues (e.g., climate change) are indeed real and indeed important. But

It's a good argument, however I think it's pretty clear to a lot of people that today's issues (e.g., climate change) are indeed real and indeed important. But to your question of why to spend on them, it's because it's going to cost us a lot more (and not just money) down the line if we don't address it.