Right. You can add anyone you want to your own trust list, and no one is going to stop you from doing that. If you want to add only your friends to your trust list, you are welcome to do so. If you and your friends want to have personal trust lists made up of only the most prolific scammers on the forum, you are welcome to do that too. What you can't expect is for everyone else to sit by and let you and your friends add these scammers to the Default Trust list, and therefore directly cause harm to newbies who do not know any better.

You can have any trust list you want, but if you are going to have a completely irresponsible one, expect to be excluded from DT. It's as simple as that.