We're the universe trying to learn about itself. We have the duty to be best ones we can be. Agree that on the cosmic timescale it's meaningless. On the individual level it's not.
Or you know everything there is about infinity, other universes, how and where where "the playground" is placed (what's beyond its borders), what's the origin/meaning of life and so on?
Everything is meaningless and therefore we can do what we like? Even if it has no meaning to you, are you sure (deep down) it has no meaning for the lives you're taking (with your food choices)?