Not a big deal and entirely avoidable, issue with Binance old cold wallet inputs still being valid on both chains is just due to lack of strong replay protection (see "tainted coin").

This was fixed in BCH back in Aug 2017 with deployment of SIGHASH_FORKID, this is sighash flag which basically makes tx signatures dependant on the network they are being broadcast on, meaning a tx valid and signed on one chain will be invalid on the other. It has been standard playbook for basically every fork since BCH to use SIGHASH_FORKID for replay protection (eg. BTG did same, just with a different forkid number).

It is surprising that Blake2b is still using opt-in-only protection after almost 3 months. Normal signatures are still fully replayable, so it is still possible because whoever wrote the fork did not include the strong mandatory version which has been best practice for almost a decade. Hard to take such fork seriously as being the "real" one when they make such elementary errors.

Imagine the case where someone spends his bitcoins and unknowingly the tx is replayed so the forkcoins are moved and burnt this way. A while later that same person tries to claim his airdrop but he realizes he has none so the shitcoiners have 1 less dump to worry about therefore their shitcoin's price can remain a little bit higher than if that tx was not replayed.... win for the shitcoiners perhaps?

It was hard to take them seriously the day they decided to fork off with a minute percentage of the hashrate.

Yup.
I once thought this was just Luke's ego and they did it so they can claim their chain is still the original Bitcoin, but after a lot of stuff happened and Convoy started mining, Luke and Guida's crusade against Chinese miners, their desire to invalidate coin rewards for toher miners and so on, it seems like it was all about money, so Maxwell was right: