But you claimed that protesters demanding a solution were a problem, or that they were unjustified because they couldn't offer a solution. Why would people have to present a solution in order to demand for their future to not be destroyed?

After all, "solving climate change" is technologically a solved problem. Humanity has all the technological knowledge to switch to carbon-free energy production. The problem are the costs of that switch based on current technology. But if we can't reduce the costs further, that still does not invalidate the demand of protesters who don't want to be stuck with paying the massive price of having to deal with a broken ecosystem later. It's still a perfectly justified demand that current generations pay in order to avoid costs for future generations.