It isn't bad to investigate or ask questions; the problem is that many of the people who are vocal proponents of the lab-leak theory are making a motte and bailey argument that takes the form of "the virus escaped from a lab in China" as the motte and "China deliberately released the virus to hurt its enemies/Trump/etc" as the bailey. I don't have a strong opinion on the origin of the virus, but the idea that China released it deliberately is very stupid and where most of the lab-leak conversations I've followed end up.

It also doesn't help that China's current leadership is extremely allergic to anything that implicates China at all, so their actions are largely compatible with what you'd see in a coverup.