No one claimed that it's for the benefit of the rest of the world. But the reality is that if US drug prices were fixed by the government at lower levels then there would be less new drug development. The US develops around 75% of world's new drugs. Would you prefer to have fewer new drugs going forward?
Nope. Nobody changed the argument. No one said "USA subsidizes drug development out of a societal sense of charitable obligation to the rest of the world." It just so happens that - due to the unfortunate design of our system - the rest of the world is receiving a subsidy.
In fact, there are European-HQ'd pharma companies that also make the lion's share of their profits in the US - so that's certainly not benefiting the US.
