A virus can cause up to 6 or 8 hours of work to be lost in re-installing or re-configuring the OS and the applications.
A trojan or backdoor program can spread to all the other machines on the LAN, costing untold amounts to fix and compromising security including personal information of employees and trade secrets, which once disclosed cannot be made trade secrets again.
If you truly don't grasp the parallel between a defectively designed auto and a defective software design, I feel sorry for you.