“Well, if a Catholic can get to define Protestantism for Protestants, then Protestants can get to define Catholicism for Catholics.”
No. For two reasons:
1) Only the orthodox can make definitions. Hence Protestants cannot.
2) Protestants defined themselves in the 16th century with their doctrines - defended here by Protestants all the time.
“Otherwise, Catholics are operating on a double standard, which I see is really not very unusual.”
No, we simply operate on one standard: Truth is truth.
Are you Orthodox or Catholic?
If you are Catholic, you can not make definitions by your own admission.
That 16th century statement is false.
Protestantism started about 1,000 years ago when the Orthodox decided to follow Scripture and not acquiesce to Catholicism and their "created" popeatry.
They refused to kowtow to the Catholic's pope and so Catholicism PROTESTED against their decision and so Catholics are the FIRST Protestants.
Then a few hundred years later a Catholic started a movement to move closer to Christianity, Holy Scripture and Jesus and thus was started what today is called Protestantism.
And eventually Catholicism accepted the Orthodox as part of their popedom, and now call them Catholics.
It was a financial decision on the part of the Catholic mucky mucks.