Basically, the value of unit-testing everything drops considerably when you move from OO to writing mostly side-effect free code and testing expressions in a REPL. That doesn't mean that unit tests become worthless; it means there are more cases where they aren't worth doing because their cost exceeds their benefit. One area where the benefit does still exceed the cost, in my opinion, is when you're working with complex algorithms. But that's a far cry from test-everything.
The weakness of the test-everything school is that they don't take into account the cost of writing and maintaining tests. They act as if the benefit is non-trivial and the cost is trivial, which is why they think something's wrong with people who don't agree with them. But the cost isn't trivial.
Basically, the value of unit-testing everything drops considerably when you move from OO to writing mostly side-effect free code and testing expressions in a REPL. That doesn't mean that unit tests become worthless; it means there are more cases where they aren't worth doing because their cost exceeds their benefit. One area where the benefit does still exceed the cost, in my opinion, is when you're working with complex algorithms. But that's a far cry from test-everything.
The weakness of the test-everything school is that they don't take into account the cost of writing and maintaining tests. They act as if the benefit is non-trivial and the cost is trivial, which is why they think something's wrong with people who don't agree with them. But the cost isn't trivial.