Another take:

The happy rider, is a conspiracy theory enjoyer. Happy in the "knowledge" that someone (anyone) is at the controls of the world, it gives comfort in a perverse way. Even though they know that the "controllers" are doing bad things.
The sad rider, is a realist. Can see that they are stuck on a trolley that is currently plowing through people, their personal actions mean nothing in the aggregate of all other actions in the world. They saw that the person at the leaver chose to keep themselves pure, rather than reduce the suffering in the world and taint themselves in the process.