I disagree, but let me clarify. I mean security in terms of an OS which is robust and not full of bad programming techniques, hence it has very few exploits. This has nothing to do with performance but with design and construction techniques.
Me again

You going on about something else

I still
disagree with you but let me be more clear in the point I am trying to make.
I am not talking about anything (device, OS, application) specific when I am talking about security & performance, merely of the simple process of enabling
a security-based function on
any type of device, whether it be IPSEC, NAT, SSL, etc. on a router, switch, PC, etc.
This WILL affect performance due it requiring more processing power as opposed to when it was not running.
Admittedly, the performance should not be noticeable, especially enabling IPSEC on a 6500

but I am simply making the point that in the simplest sense, security affects performance. Bottomline.