Yes, it is a theory, cause in real life it just ain't so.
Guess it depends on what the meaning of 'is' is.
REAL LIFE: US Sen Harrison Williams (D-NJ) lost his seat and went to jail b/c he took a gift of stock (in a sting setup with an Arab sheik).
Ordinary citizens can take gifts of stock without penalty.
When an elected offical does so, the implication is that he will use the power of gov’t to benefit the gift-giver.