Don't use a license you don't want people to exercise. In fact I don't quite understand why you would open source the project at all if you are going to actively discourage people from using the code in ways that are permitted by common open source licenses.

If you don't want anyone else to make money from the project perhaps designing your application in clear parts and releasing them as open source libraries would have made more sense. Releasing the whole thing as open source, encouraging contributions while wanting to be the only one able to profit from said source seems wrong. Wordpress don't stop others making money from hosting.

We've added an MIT license without a disclaimer, people are free to do whatever they please with it.

So you'll give us the permission to go commercial with your code and call us jerk if we actually go commercial?

He grants the rights to go commercial with their code, but reserves the right to call us names for doing so. Still sounds like a good deal to me.

Name-calling rights are far too often forgotten in modern day contracts, I'm afraid...

I think that's one of the barriers that prevents code from being released: People (like myself) worried that others would take that code and compete with you.

Than use a different license that explicitly forbids that. Or force them to get your permission first. Using an open-source license is not mandatory