I've noticed much trinitarian error falls into two categories:
1) they make passages say more than they are intended to say
2) they assign nearly scriptural credence to non scripture. You mentioned a strong example in Athanasius, but I'm thinking also of early councils in general (which I believe often amounted to power plays which Jesus would have disapproved of) and modern majority opinion
I tend to give extra respect to church fathers of the first three centuries because they lived during times of heavy persecution and spoke Greek. But once Christianity became the official religion of Rome, I sometimes wonder if many would-be doctrine creators had, in a sense, "too much time on their hands" and came to prefer complex and mysterious doctrine with tenuous scriptural support such the trinity, inherited guilt, immaculate reception, along with many others.
