You misunderstand. Internet is not a magical no-law zone.
And no one said that it was.
When twitter opens an account with a EU citizen, this transaction happened in the EU.
For the European, perhaps. Twitter didn't go anywhere. That EU citizen sent a request to a server west of the Rockies.
They are bound, for this account, by EU law.
No, they're not.
Your whole argument is that this is unworkable.
That seems to be an exaggeration of one argument he used.
In fact, it works very well:
In fact, it doesn't. If it did, there would be no Twitter, because Iran, China, and North Korea would kill it.
laws are mostly compatible,
Not at all compatible.
and citizens are mostly allowed to do as they please in the privacy of their own homes.
You know, when you say shit like that “as they please in the privacy of their own homes,” it makes Americans want to free the shit out of you, too. You should do as you please anywhere so long as it does not interfere with another's ability to do as he pleases.
Once in a while, there is some incompatibility, and it needs to get resolved. But the greater point is that you, US citizen, do not lose rights because you use a Chinese website,
That's just a non sequitur. “Lose rights?” You mean like the right to make contracts, to bargain for a service according to mutually beneficial terms? (Like Twitter's supposedly illegal-in-a-foreign-jurisdiction-where-they-have-no-operations terms of service?)
nor does a EU citizen loses his when dealing with twitter.
And no one claimed he does.
This, in turns means that when twitter agreed to provide a service to a EU citizen,
They didn't agree to provide a service to a [sic] EU citizen. They agreed to provide service to a person. They don't ask nationality (and they shouldn't have to and never should).
they also agreed to abide by EU privacy laws.
If someone in Germany calls me on the telephone, am I agreeing to follow German laws? No. Bullshit.
In practice, this is incompatible with US law, because there, citizens have less [sic] rights.
(1) Fewer rights.
(2) Bullshit. In the US, people (not even citizens, immigrants, too) have the right to create companies like Twitter without having to have a dozen lawyers in every country around the world to maintain a 140-character microblogging site.
Again, in practice, this means that twitter ought to have a twitter EU subsidiary which does the data collection and management for EU citizens.
No, it means they shouldn't if they don't want to quintuple their expenses.
And for technical reasons,I also expect them to do that anyway.
If you are a tiny company, this sucks, and you will have to decide which country enforces the stiffest penalty... But again, usually, this poses no problem. And if you cared about the privacy of you users, there would be no data to subpoena anyway.
(1) Without those data, Twitter could not operate. That's like an airplane with no engine.
(2) It was a warrant, not a subpoena. (They wanted data, not testimony.)