As Watchdog said, what you're suggesting there isn't allowed by the license either, so why should mIRC add a feature that is specifically designed for people who want to break the license agreement? And you're right people already do find ways to use mIRC for trojans, but does that mean we should make it easier for them? Your argument is:
1.) People commit crimes
2.) Regardless of what mIRC does, people will commit crimes
3.) Therefore, mIRC should not try and stop people from committing crimes
That seems like flawed logic to me. By the same argument someone could say the police force should be abolished because people are still going to commit crimes whether there are police or not. Just because someone will commit a crime doesn't mean you have to make it easy for him/her.