Sport Pilot inconsistency

I am unclear on two Sport Pilot issues: First, a new pilot may qualify
for a Sport Pilot ticket even though he or she takes a medication that
would preclude a 3rd class medical. However, an experienced pilot with
a higher ticket may not operate as a Sport Pilot if he lost a medical
last year for taking the same medication. In other words, both pilots
have exactly the same medical history: One is allowed to fly as a
Sport Pilot and the other is not.

For the second issue, let's assume the medication is an SSRI where the
preponderance of medical opinion is that the medication does not
impair a pilot and makes them less of a risk if they need it. This is
the same medication that has been commonly prescribed to combat Navy
carrier pilots and Canadian fliers for years without issues. The same
medication that was prescribed for the ATP who will fly your family
home for Christmas but he cannot take it out of fear of losing his
medical.