So according to you, the presence of VOLUNTARY Tattoos that the defendant wanted and requested be placed on his body are not allowed? What next? wigs for skin heads?
If tattoos are relevant to the trial, then the judge could prevent the defense from covering them. "I remember the robber had a big "Z" tattooed on his forehead." The defendant has a big Z tattooed on his forehead. That would probably be viewable by the jury on the issue of identification.
If tattoos are NOT relevant to the trial, and would be prejudicial, then they should be covered. In the case mentioned in the OP, it sounds as though the tattoos would NOT be relevant. In such a situation, irrelevant tattoos showing the defendant is a skinhead, would clearly be prejudicial. The jury might convict the defendant solely because they don't like skinheads, rather than because of the actual evidence.
So, to answer your question, yes - in this case, the presence of (irrelevant and prejudicial) VOLUNTARY tattoos are properly not allowed.
Following your logic, if a defendant VOLUNTARILY belonged to the Hell's Angels, then that fact should be presented to the jury in a case where the defendant is on trial for writing a bad check.