Your story of the green and red apples is interesting, but it misses an important aspect of health service utilization - out of pocket payment. There's nothing new in users switching from uncovered to covered services. Many studies found the net effect is roughly zero. However, if people can have the same volume of services but pay less, that should improve their welfare. The literature on health shock and consumption smoothing in developing countries suggests that high out-of-pocket payment could have an impact on nutrition status and other outcomes that we care about. Establishing a rigorous causal story is undoubtedly challenging but it doesn't mean that the effect doesn't exist if 3 studies didn't find it.