The contradiction is that breaking up Google and Amazon would also destroy categories of business where the United States is dominant over other countries.

Prevent them from buying their competitors, for sure, but don't kid yourself into thinking that there are many neat ways to parcel these companies up into neat little independent business units. There is at best a very small number of ways to do this and the government will not get it right, just look at their most recent attempt with Google to strip out Chrome of all things.

Just to be clear on my stance,I agree that blocking the irobot deal was absurd. Context matters in a big way, clearly they were struggling and were basically alone in the market as an American company.

I think you also need to apply that context to Google and Amazon and consider whether the government would do so wisely.