I think that in many cases tatoos have sin behind them as in associating with groups/people that are sinful or ideas that are ungodly.
So what? Unless you also propose that Christians refrain from speaking or writing the common names of the days of the week or several of the months of the year, all of which honor pagan deities, your observance of this principle is inconsistent.
Besides, "many" =\= "all."
In the Bible it equates it wrong to do things to make your brother stumble (sin) and tatoos can be a source of that in some cases.
That is ONE principle presented in Scripture. Another is that it can be good to refuse to submit to strictures that *appear* to be wise but really are not. Besides depriving oneself of the freedom Christ purchased, it can wrongly convey the idea that Xianity is about following rules.
I think that often the idea behind tatoos is to get attention and in that getting attention the desire behind it in the end is to sin in the effort.
How exactly does one dress, wear one's hair, etc. so as NOT to "get attention." You could be "plain" as many Anabaptists and some Free Methodists, but by its contrast to the practices of common culture, that in itself attracts attention.
Christians are not commanded against tatoos, the Jews as they were to be a set aside people of God that were not to be seen as individuals but a nation. tatoos can be a source of division more than uniting people as a whole.
Neither the exact nature of the marks, nor the reason people got them, is really known. The word is literally "imprints." In addition to conventional "tattoos," it probably included face- and body-painting, and possibly branding. It may even be directly linked to scarring from the body-cutting in the previous portion of the verse. I guess just to on the safe side, we should proscribe face- and body-painting at sporting events and fairs.
You're right that a major purpose of the Law was to distinguish the people of God from "the nations." That was under the Obsolete Covenant. We are under the New Covenant. We are explicitly told we are distinguished from the world at large by two things: Love for one another (John 13:35) and the presence of the Spirit (1 John 3:24; 4:13; Rom. 8:9).
The Bible also equates our body as the temple of God, and tatoos can be considered a form of advertising or graffiti and nobody would want their "temple" to have such nonsense on it. Imagine what your church would look like tatood all over it with everyone putting the tatoos off their body on the outside walls and see how those who attend quickly want to paint over them all.
Yeah. And let's get rid of the stained glass windows. And any pictures of angels, 'cause someone might mistake them for valkyries and "stumble." And any crosses, 'cause someone might think it's a representation of Thor's hammer, or of the tree Odin was hanged on for nine days to gain the wisdom of the runes.
If your *intent* in getting tats is to honor some pagan demon-god, or to associate with a violent gang or racist nuts, then get them, but don't pretend to be Xian. If your intent is to get them because you like the way they look, or to demonstrate the Xian freedom from the useless elemental principles of life under law, get them and wear them with joy.