Key reuse
It is important to realize that the security of the Monero network and your own Monero is dependent on the security of your Monero keys. Your Monero keys are MONERO keys. Do NOT use them for any other purpose, including claiming coins from a Monero fork. Using your keys to spend the same outputs twice on different forked blockchains will damage your privacy, and others', as both spends will bear the same key image, but different rings, with only your spent output in common (this does not impact stealth addresses nor confidential transactions, just ring signatures). Moreover, by using such a "same keys" fork, the security of your Monero private keys now depends on those third parties.
Forkers, if you're forking Monero, DO NOT ask users to reuse their Monero keys, but have them create new keys for your fork.
Users, if a forker asks you to use your Monero keys for their fork (after this notification is published), they're trying to manipulate you into being part of a large scale attack on Monero.
Be safe, and don't reuse your Monero keys for any other purpose than using Monero.