Yoong Liat wrote:
Can I conclude that my friend's explanation is not acceptabe?
As stated yes. The "subject" of the sentence is not negotiable as explained.
But your friend is on the right path, sometimes a plural word is used to express a singular entity in meaning (explained as a single "scenic spot" by your friend). What your friend is trying to teach you is to try to discern the intended meaning (not the "subject" as this is a grammatical term) of the subject of the sentence. Does the intended reference want to prioritize the individual entities within a group or the group on the whole?
To give an unrelated example I'll use the word "people", which as you know is already plural. My students would often ask me if "peoples" is ever correct and it, in fact, is when you speak of distinct groups of people.
For example: "I met many interesting people in my travels". vs. "I have met many interesting peoples in my travels".
As in this case, it all depends on what meaning you wish to convey. But with proper nouns traditional collocation generally reigns and you'd sound funny if you conjugated differently than tradition dictates.
Note: FreeDuck is correct in that this is a case where usage often differs between UK and American English. And the given sports team examples help delineate such differences.