I disagree with most of the other answers, which are basically telling you that it's unethical and you shouldn't do it. Their reasoning is sound and conservative, but overlooks the basic idea that this is an act of protest.
Yes, it is unethical to add your baby as a co-author. However, you believe that you are already being forced to do an equivalent unethical action by your group. In effect, what you are doing is planting a signpost that says (without being explicit), that you are aware of the unethical actions that you are taking and protest against being forced to do so.
This is a risky stance to take, from a professional career perspective, but from a legal and ethical perspective you are doing nothing worse than you are being forced to do already. It does, however, change the situation slightly for each of them:
- You are more likely to face consequences with the publisher, because a completely implausible author makes the unethical co-authorship more likely to be detected .
- I think you are actually in a better position ethically, since you have declared your disapproval of the behavior that you consider unethical.
I would thus judge your proposed course of action to be an ethical act of protest of an unethical situation. It would be better to get rid of the unethical coauthors in the first place, but if you cannot do that, this is within the reasonable traditions of scientific defiance (F.D.C. Willard being another example, as are the uses of SCIgen).
You need to be aware, however, that doing this is likely to create enemies out of everyone in your research group, and may end your scientific career. That is a reason that many people would choose to not make a fuss about the unethical co-authorship and instead perpetuate the problem. Only you know how important your personal goals are, and whether this act of protest is worth the likelihood that you will make enemies and may destroy your career. From an ethical and legal standpoint, however, I think that you are fine.