There shouldn't be a debate at all since both sides are technically correct. Here's the definition from Google:

> dec·i·mate /ˈdesəˌmāt/ verb 1. kill, destroy, or remove a large percentage or part of. "the project would decimate the fragile wetland wilderness" 2. HISTORICAL kill one in every ten of (a group of soldiers or others) as a punishment for the whole group.

There are many words and phrases that have changed in meaning over time through popular (mis)use.