Why don't you try justifying that one? Because I posit that if the French government didn't exist the market would exist anyway.
Without a government the only way of maintaining your wealth is being a warring faction. Those rarely require advertising online.
Anyway, the ultimate authority on which taxes and to what percentage will be imposed is the guy with the most power to execute decisions in the country. In France, that guy is the France government. You may think that this particular new rule is unfair, but I think the lawmakers do not care. There are already many taxes that are unfair from certain points of view, such as income tax. Life in a country run by a government is not fair, if you interact with the country, you have to obey its laws, the government is not interested whether you agree with them (that is, unless there is many of you so you can get together and put pressure on the government).
(Also, arguably, French eyeballs are a resource belonging to France, which Google exploits.)