Said tax and trade agreements don't impose fairness and order, as much as they tie every participating nation down in a race to the bottom. Any board of directors would be considered to be out of their minds if for the sake of a single, non-critical contract, they signed agreements that completely tied their hands in how their firm should run. On the other hand, when governments do it, they are heroes.

Disclaimer: I'm a Canadian working for Google. And I have no opinion on this particular piece of legislature.

There is a difference between a territorial tax system and tariffs.

If properly implemented, territorial tax systems do not create a race to the bottom, because countries compete for the quality of service they can offer to businesses that operate there. In theory, a rich individual could live in a tiny country with no income tax, but the moment they tried to put that money to work, they would have to operate in some other country which imposed territorial taxation.

On the other hand, this law is more like a tariff. It seeks to impose a tax on value created (i.e. the selling of an ad to an Italian business) whether or not that value was created in Italy or not.

"And the deeper problem is that every country would like to shift its tax burdens to "big multinationals""

This is of course, 100% the problem. None of these countries seem to believe they can support themselves long term on the tax revenues earned by just their local people and businesses.

If that's really the case, they are doomed, long term, without changes.