So are humans (we breathe out CO2 constantly!). A process emitting greenhouse gases is not an inherent reason to eschew it, so long as the entire end-to-end process isn't net-positive.

Use that compost to fertilise a tree, and you are still net negative on carbon, versus sending those food scraps to the local trash incinerator.

It's all a cycle, They put carbon in, they release carbon out. At least the average American is doing a commendable job in increasing their personal carbon sequestration.