It's not the only way. We could keep eating grain but stop the multiplication of humans on the planet.
But technology won't solve the problem that if human eating habits stay on the current trajectory, they will eat 50% more grain.
I get it that this is not what you meant. But the progress of technology, while you can rely on it getting somewhere, is unpredictable. It'd be foolish to count on it without considering contingencies in case it doesn't deliver.
I know it's good to always hedge against risk. But to hedge against technological progress is shorting humanity as a whole and is a dark place to go. Arguments of type "let's reduce population" nonetheless stem from that line of thinking as you eluded to.
I don't see how hedging about development of a particular technology is a bad thing. We have expected CPUs to get faster, but it didn't get there. Some people were presumably hedging against it, and now we've routed around this with multi-core computers.
People might have expected flying cars, yet they didn't come to be. Instead, quick communication has been solved by the Internet.
The world has many ideas, and they can be explored simultaneously, but we also must face the possibility of failure in case we paint ourselves into a corner, like we just did with the global warming. I find broad exploration rather optimistic compared to being single-minded about something happening in the future.
But technology won't solve the problem that if human eating habits stay on the current trajectory, they will eat 50% more grain.
I get it that this is not what you meant. But the progress of technology, while you can rely on it getting somewhere, is unpredictable. It'd be foolish to count on it without considering contingencies in case it doesn't deliver.