It is usually considered unethical to modify other people's data without their authorization. In many countries this is also illegal. Copyright and Ownership Problems. In many cases, modifying a particular program could mean that copyright, ownership, or at least technical support rights for this program are voided. Psychological Reasons Trust Problems.
Users like to think that they have full control on what is happening in their machine.
Negative Common Meaning. Summary While frequently discussed, the general consensus is that there is no task that requires a virus.