Are you an infidel?
Is it a good thing to be calling yourself an infidel?
This is a common derogative term used by Islamist to label those who do not accept their religion,
Kafir (Arabic: كافر kāfir; plural كفّار kuffār; feminine كافرة kāfirah) is an Arabic term (from the root K-F-R "to cover") meaning "one who covers the truth" a person who rejects or disbelieves in God and the teachings of the Islamic prophet Muhammad, and denies the dominion and authority of God
And people who leave Islam are called Infidels. When they leave they may be asked if they are an infidel, and knowing that they no longer hold to that belief system will likely answer yes.
If they now believe in God our Father in heaven and the Lord Jesus Christ (He who was born without sin and died for us) and if they have put their trust in Him. They are not Infidels (unbelievers) according to Scripture.
This is much like the derogative term (Protestant) given by the Catholics to those who left Catholicism, and so today many people continue to call themselves by this term (I am not a protestant. I am not protesting Catholicism I am a Christian).
To be calling yourself an unbeliever or a truth denier or a God denier when you mean you are not a believer in the Islam faith and Islam prophet is not a good thing. You hopefully are a Christian. It makes no sense to be applying someone's derogative term to yourself just because they prefer to call you by that derogative term.