The thing is, we're at a point where any reduction or slowing of Co2 is a victory, and can at the very least buy us (especially the populations most effected) a little bit more time to get our collective shit together against the big polluters.
But we don't know when that time will come, so we need to do as much as we can until then. We know the billionaires planes will continue, but we can at the very least prevent some of our own emissions from compounding with them. Us doing our bit is not negated by the billionaires not joining in with us. It's not fair, but the climate doesn't care about fair, it cares about total emissions.
So let's chip in collectively to slow things down, even if only slightly, until we can slow it down a lot. :)