In high school, I made an argument just for the sake of it in favor of astrology about electromagnetism and/or gravity as well.
I didn't believe in it, but I made it anyway.
Tarnas' view of astrology makes those kinds of arguments completely irrelevant.
And the guy is brilliant. His book on the history of western philosophy is amazing.
But this is also Tarnas' point: that understanding astrology, actually separating truth from illusion, requires a far higher level of critical intelligence than is required for scientific understanding.
In Tarnas' view, one must be able to use critical thinking to separate confirmation bias from actual, genuine correlation.
We might not be able to verify these actual, genuine correlations via tests, but that doesn't mean they're not true.
Absence of evidence ain't evidence of absence, just cuz you didn't see it doesn't mean it didn't happen.