It is a very sound theory, and it does apply in this case as it is theory ground in linguistics (ie. Text, speach, language). Sure you've acknowledged that good people come from all backgrounds, however that doesnt change the fact that you have set yourself up a binary opposition by positioning yourself as a 'god fearing christian'. This is fair enough, thats your faith, and im not going to argue that. It could be right, it could be wrong. The IMPORTANT fact that i am stating is, by claiming this christian position, you have created an opposing postion "non-christian". By claiming the virtues of 'good' as christian, you instantly impose the negative thoughts of 'bad' to those that are "non-christian".
As Nerevar states, saying you're a "moral person" carries a whole different meaning, both explicitly and implicitly, than saying you're a "Christian" and assuming that makes you a moral person.