His reasoning is valid. Compared to the S&P500, it's a small sum of money. Most people aren't buying a fund that tracks that nasdaq index. The total effect isn't that large.
His reasoning isn't valid.
Not only is he wrong that it doesn't impact him, because VTI is impacted, but the whole premise is wrong. "I'm not harmed" does not mean things are fine. If I go murder your neighbor, will you come to my trial and demand I go free because you weren't harmed? Should the judge let me go because he wasn't harmed?