Recentness
"Jethro Tubbs was proud to fly the Confederate flag until the day he died."
If Mister Tubbs died in 1882 then perhaps one could understand his position. He had probably grown up in a society where slavery was the norm, maybe even fought under the flag... lost comrades. Maybe he sacrificed a limb for the flag.
If Mister Tubbs died in 2012 then he was a straight up racist crackpot.
Issac Newton believed a lot of strange religious/mystical numerology stuff, but was the greatest physicist of his time.
If a major physicist published any of Newton's late writings today he would be finished as a physicist and urged into early retirement.
The greatest scientists in the world did not believe in evolution in 1800. In 2012 rejecting evolution is prima facie evidence of not being a scientist at all, let alone a great scientist.
It makes a difference how recently ideas were advanced.
The sky is not a metal dome, and never was, but not all statements that it is a metal dome are interchangeable. In 2000 BC that was a reasonable statement. In 2000 AD it is not. granted, both statements are equally false as cosmology, but they are not fully interchangeable for what they say about the speaker.