Thank you, Charles, for backing up my main point from my post yesterday.
Cardano's fork made double-spending possible. Users of the malicious fork can get their transactions reverted when the fork is orphaned later, and this creates damages.
Major damages can include
1) exchanges and their users being defrauded when interacting with one another during deposits/withdrawals (as explained below by Charles),
and
2) bridges malfunctioning or depegging if the reorg length is outside of established norms (as well explained by yesterday).
Point 2 is especially relevant to us at , who are trying to allow any token to move between Bitcoin and Cardano.
An 846 block reorg is *bad.* We and others have to be prepared for edge cases where reorgs like this happen, but sadly, many won't be ready.
It's good that the network and community came together to roll out a fix. Again, not the end of the world; they can grow from this.
Just want us all to recognize the severity of the problem. 
Quote
Charles Hoskinson
@IOHK_Charles
Replying to @phil_uplc and @AThrouvalas
The forks can't talk to each other. You can spend the same money twice and if the transaction settles gain something of value. Second, you can deposit on an exchange, clear it and then buy some with the orphan ada and withdrawal.
For a massive chain reorg, this is a real threat