My Hebrew professor, in discussing the etymology of some words has been known to contemptuously spit out that the root comes from "the Indo-European storehouse". He's not exactly a purist, but I can see the problem. Why borrow words from a system that doesn't really meld well with your own? Especially when these words aren't particularly complicated semantic undertakings. Though, some languages like to borrow. It's what they do (I'm looking in your direction, English. You're pretty much willing to invite any morpheme into your bed, aren't you?)
So, that said, borrowing a word here and there doesn't seem like such a problem. But, what if you're Greek? And, say, it's the 5th Century and you've created small things like drama and democracy and vase painting and Classical architecture. Why on earth, when you were smoothing things out like this didn't you bother to regularize the word for "to carry"?
Remember how you guys did the Golden Mean? And even went so far as curving parts of the Parthenon so it'd look straight? Yeah, you have a thing for order. That's cool. But, seriously, order begins at home.
For those of you reading who don't do Greek, here's how the verbal system works, at least theoretically. When you learn a verb, you learn six principal parts, related to different tenses. This is partly because ancient languages are needlessly complex at even their most regular bits, but also because the rules are sort of mishmash and it's generally easier to just memorize things.
So, a nice, regular verb looks like this:
παιδευω, παιδευσω, ἐπαιδευσα, πεπαιδευκα, πεπαιδευμαι, ἐπαιδευθην
Even not reading Greek, you can see this guy "παιδευ" sort of hangs around and gets stuff added to it.
Then, there's φερω, the word for "to carry". No real problem there. But then you look at the other forms which come out:
οἰσω, ἠνεγκα, ἐνηνοχα, ἐνηνεγμαι, ἠνεχθην
WTF? Three DIFFERENT roots? Sure, just pull anything you want out of Proto Indo-European. That's a good choice. Oh, and while you're at it, could you chose one root that likes to lose part of itself sometimes? That'd be swell.
I hate you sometimes, Classical Greek. Sometimes, I think you should die in a fire. Or, y'know, at the hands of the Romans. You pick.