If you see one roach, there are surely 1000 of his brothers you dont see.
"Tip of the iceberg" is not an axiom, it's a metaphor.
When applied to the IRS scandal, it's a metaphor that's axiomatic, I'll grant you.
But you're right, I agree with you. An iceberg is a clean, proud thing, a beautiful manifestation of nature's majesty.
The cockroach metaphor is much better.
That’s all well and good, but why insult cockroaches?