It is not taken away from them and cannot be taken away from them. Just like you can solve any puzzle you like even if there is already a solution.
This is evidenced by the scant few people who get into math just so they can rediscover group theory or differential calculus on their own with no spoilers.
The argument was about mathematicians, and "anyone who got into mathematics for love of solving problems".
We're not talking about doing it as a hobby.
Or did you think the argment was that they'll be forbidden by force to do math, and come to refute that?