From what you have written, regarding Christians using the Laws of Moses to condemn others and citing shellfish, pork and tattoos, I get the impression that you are a new Christian who either has tattoos or is thinking about getting a tattoo or maybe more tattoos.
First, let me share an anecdote about condemnation. One day, as a volunteer, I was helping paint out the inside of a church before the daughter of a former pastor of that church was to be remarried after having been divorced. Somehow, I knocked over a four-gallon pale of white paint that flowed over the red carpet that ran down the aisle in the middle of the church. The mother of the woman being remarried tried to put a guilt trip on me for spoiling the carpet. In other words, I was supposed to feel condemned. However, I did not feel condemned because I knew I had done nothing wrong. An accident occurred because someone else put the paint behind me and did not tell me it was there. Instead of accepting the woman’s condemnation, I informed her that I was sorry for the accident, and if she liked she could forgive me, but I was not going to have a guilt trip because she wanted me to have one. (I could have responded in a similar manner abusively and called her a self-righteous, hypocritical bitch—but I had no desire.) The reason for my actions is found in the following Scripture:
Little children, let us not love in word or speech but in deed and in truth. By this, we shall know that we are of the truth, and reassure our hearts before him whenever our hearts condemn us; for God is greater than our hearts, and he knows everything. Beloved, if our hearts do not condemn us, we have confidence before God (1 John 3:18-21).
If we are truly Christian, we will seek the Lord God and not condemn others by laying guilt trips on them, since we know we are all in the same boat. The truth is we have all come out of the sewer of sin, even if there are some like myself who require more washing to remove the stain of sin than what others do.
For we ourselves were once foolish, disobedient, led astray, slaves to various passions and pleasures, passing our days in malice and envy, hated by men and hating one another; but when the goodness and loving kindness of God our Savior appeared, he saved us, not because of deeds done by us in righteousness, but in virtue of his own mercy, by the washing of regeneration and renewal in the Holy Spirit, which he poured out upon us richly through Jesus Christ our Savior. (Titus 3:3-6).
The real issue is the reason a Christian would want to have a tattoo in the first place. Why would a Christian want to have a tattoo?
If a person wants a tattoo to identify with the world, then the person should get one. If a person’s heart's desire is to have a tattoo, nothing will stop the person from doing it. If the person is getting a tattoo because of some faddish reason, the person might be ambivalent and open to feeling condemned, whether a Christian or not.
For a Christian who desires to do what God desires (come to the full knowledge of the truth) and reap the blessings, there is no need to have a tattoo; therefore there is no desire or conflict in respect to tattoos within that Christian's heart. For any person claiming to be a Christian, it is worth bearing in mind that to identify with the world is to be an enemy of the Lord.
Unfaithful creatures! Do you not know that friendship with the world is enmity with God? Therefore whoever wishes to be a friend of the world makes himself an enemy of God. (James 4:4)
Many will scoff at this, but people who are getting tattoos are being prepared for acceptance of the mark of the beast prophesied in the book of Revelation. Tattoos were anathema not so long ago among the majority of the public herd of goats (that is what Jesus calls the unsaved), and they were seen only on those who were rebellious and anti-establishment. However, the powers-that-be decided to pay some celebrities a couple of million dollars to get tattoos and now the goat herd is following suit and most of the goats are getting them because they are fashionable.
The next move is to pay a few celebrities to take the chip and then, once more, the herd will follow and the goats will revel in the opportunity to be more entangled in the rope of no hope; just so they can gets some stamps or digits to permit them to buy and sell in the Orwellian world of the Beastly Big Brother, of which a certain number represents his name (probably the name of the corporation).
Also it causes all, both small and great, both rich and poor, both free and slave, to be marked on the right hand or the forehead, so that no one can buy or sell unless he has the mark, that is, the name of the beast or the number of its name. (Revelation 13:16-17)
People who claim to be Christians and who want to identify with the world are not really looking to receive what Lord Jesus Christ has for them. This does not mean that people who have tattoos are going to miss out. Repentance is always an option. On the other hand, those who would rather have a tattoo instead of seeking Lord Jesus to find out how they can grow in knowledge and faith are showing where their heart is at. “If you love me,” says the Lord, "you will keep my commandments," and keep oneself unstained by the world.
Unless you know the commandments and their implications, you will not know when you break them. If you are looking to Lord Jesus, your heart will not condemn you. Nevertheless, the people of God perish for lack of knowledge.