I can’t get on board with hyper-academic crap like this. Colloquial communication is WAY more loosey-goosey than anything linguists care to fuss about, and I’m perfectly OK with that.
Frankly, if someone said “more people have been to berlin than I have” in conversation I would probably understand exactly what they’re getting at. Human communication is FULL of vagaries and syntactical ambiguity yet people are still able to convey what they want to convey.
This is not to say that a complete flouting of the quote-unquote “rules” is okay in all instances (“gazpacho” anyone?), ESPECIALLY when a person is being smug and trying to sound conspicuously smart (and I concede that I have trouble taking seriously anyone who mixes up “they’re/there/their” or misuses an apostrophe to pluralize a noun), but I think it’s a waste of time to get hung up on so-called “Escher sentences.”
You know, questions like this are really important and more than a curiosity to interpreters. People actually do make ungrammatical statements a lot. Practically always. And people also confidently misunderstand others with great frequency and occasionally with consequence.
OK, so I think the precise reason this sentence is wrong is as follows:
This sort of “Noun has verbed” structure readily takes binary comparisons wth the “than” conjunction. But the structure of the binary comparison suggested by “More people have been to Berlin…” compares predicates (“More people have been to Berlin than to Nanjing”), while the structure of “… than I have” suggests comparing subjects (“He has been to Berlin more times than I have”).
So you end up with half a comparison that compares predicates and half a comparison comparing subjects, but both comparisons share the “Noun has verbed” structure and the “than” conjunction acting as the comparator.
Part of what makes it a weird statement though is that if you interpret it to mean “more people have been to Berlin than just me”, it would be a pretty bizarre statement to make in most contexts–is there really any doubt that you aren’t the only person who has been to Berlin in all of history? So then you’re tempted to interpret it in a maybe more convoluted way that nevertheless would be less weird as an assertion, like “more people have visited Berlin more times than me” (said among a group of frequent travelers, say). So even though it initially seems like a simple enough sentence, when you examine it there are reasons to feel pretty uncertain about what the person actually meant unless you know the detailed context, which isn’t the case with most colloquial statements that violate some strict rules of grammar.
The sentence parses just fine if the speaker is the notional concept outlined in the (disconcertingly casually rascist/nationalist named) “China Brain”.
It becomes again nonsensical if the speaker is Douglas Adam’s “Deep Thought 2”