How does the slaughter at thermopylae reflect greek valves?

There was no slaughter - after three days blocking the Persian advance at the pass at Thermopylai, the Greek force was withdrawn.

The Spartan and Thespian contingents stayed behind to cover the withdrawal and died in the process.

This was a noble sacrifice by the two contingents, but was not specifically a reflection of Greek values - the Persians also showed great courage in the course of the battle.

Courage in battle (and cowardice) are universal traits.