The problem isn't that bats are a good disease vector. The problem is that any virus that is well adapted to infect bats is capable of operating in higher temperatures than humans can survive.

One of humans' best defenses against a virus is a fever, which limits a viruses ability to fold proteins and replicate itself. But, bats' normal body temp during activity often reaches or exceeds 40C (104F). Normal human body temperature is 36C (98.6F). Thus, the human immune system isn't well adapted to combat viruses that are found in bats. By the time our vodies are hot enough to combat the virus, our brains are cooked.

Viruses sometimes jump from animals to people but are unable to transmit further. But, sometimes, they also mutate and become transmissible from human to human, and that's a problem. The more time humans spend in close proximity to large quantities of non-domestic animals. The more likely it is to see an infection jump across species.