I agree... Give 'em the burden, and maybe a little heartburn to go with it...
My last (and final) job as an IT Admin required me to write down the various username/passwords used throughout the network, routers, firewalls, servers, etc., and give them to my (former) boss.
I got "terminated" without notice and management used the "poor job performance" excuse, even after I had received a substantial raise and a glowing evaluation not two months earlier and had managed a $250K ERP upgrade project and brought it in under budget
Anyway, my (former) boss called me up about a month after I left because he needed the passwords to the routers and firewall. I asked him why and he said "he misplaced them"... He was hoping I would "do him a favor"...
I told him it would cost them $10K for me to come back and take care of the problem as a consultant because I didn't work for them anymore...