Maybe you want to have a cup of tea instead? Way more cheap and healthy. Or buy some off-brand soda. It is just as much garbage as coca cola but at least it's cheap.
Diet soda contains sweeteners that are suspected to cause cancer. Granted, you'd have to drink a couple of liters of diet soda a day before you need to be seriously concerned, but tea has one big advantage: It contains as much sugar or sweeteners as you add to it, so there's that.
I am not discussing if soda of any kind is more unhealthy than tea or not. You can drink as much soda as you want. Just don't bullshit yourself or anybody else. You only have one argument: "I like soda, don't take away my soda from me." It is not a good argument but it is all you've got.