Blocking worms/ddos for customer for free?

[Kim Onnel <karim.adel () gmail com>]

Hello,

Currently, on our ingress, we block spoofed packets, common worms/trojans ports.

We do that for all of our customers(residential DSL, Dial-up,
Corporate DSL, and the data center hosted websites/servers), however,

For me there are 2 ways to look at it, 
if i leave these worms to come in, they would consume our bandwidth
and CPU, and on the other hand, it looks like we're giving a free
service, which in a way uses up our resources,

Its the same for DDoS, if i stop it for a customer, i'm giving him a
free a service, if i dont, its gonna wreck my network.

Personally, i block the illegitimate packets out of my network(egress)
but thats because i owe this to the internet community, even if i am
not getting paid for it.

I would like to know other providers policy about this?