2. We do not have genetic data to show that these mutations are happening. This is theory only without empirical data.
3. There's a lot of debate over the role of genetics and intelligence. It's very possible that our understanding and implementation of childhood development has a larger impact on intelligence than these presumed random mutations.
4. Intelligent people are more likely to pair with other intelligent people, so maybe there is still selection effect for intelligence. This effect could be increases as world travel means a greater geographic range for potential mates.