I am a person with more than a few modifications, fist of all every person has their own right to do what ever they want with their body. and second of all there are a lot of christians (me) who have tattoos or piercings. U might as well say it is a sin to smoke and everyone should be perfect which no one is!
(no name given)
Normally I do not respond to people seeking an argument, however you seem genuine and have a point.
My guiding verse in this matter is: There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit. (Romans 8:1 KJV)
Moreover, I do not envisage perfection in this life, only when in Heaven.
Nevertheless I expect that a true Christian with a new heart from the Lord would heed to these points:
Recognize that the Lord expect perfection: Be ye therefore perfect, even as your Father which is in heaven is perfect. (Matthew 5:48 KJV)
Recognize that we cannot fully obtain perfection in this life,
Recognize that where we are at the moment is not perfection,
Recognize that we are called to reach perfection and need continually ask our Lord for strength to reach perfection.
Responding to your points:
No persons has any rights to do what they want with their bodies, it is a democratic and modern notion, totally false, for Biblically ALL belongs to the Lord, including our bodies: For who maketh thee to differ from another? and what hast thou that thou didst not receive? now if thou didst receive it, why dost thou glory, as if thou hadst not received it? (1 Corinthians 4:7 KJV)
Surely, many Christian have tattoos/piercings, received before conversion, no problem with that. However if someone calling himself "christian" mars his body with tattoos and piercing (satanic activities) and defending this activity with pride, then his "Christianity" is in serious doubt, the Lord knows.
Smoking is a sin, like the above, for the same reasons.
To conclude, hopefully it is clear that I do not expect anyone to be perfect in this life, but I also expect Christians to admit that where they are is not good enough and that, seeking continually God's help, they must endeavour to reach perfection as the Lord commands. Getting holier every day, as it were.
I shall not enter in a controversial discussion, but I would entertain a broken heart in conformity with Rom 8:1 KJV
aymon de albatrus