gunat7, do you deny what D12 says about the three occassions the Prophet said one could lie?
If you accept that then you would put a very narrow interpretation on what those occassions mean. As others have pointed out, humans, once given an inch will take a mile. A battle can be interpreted narrowly or very widely.
The bottom line is, if you grant one exception to tell a lie and not sin then you open the gates to lying. That is why a lie is always a sin for the Christian.
That is why lying sometimes is always OK for Muslims because it is not a sin, sometimes.