Jury nullification has to be coupled with an aggressive education campaign, or it just frees individuals. To get the law overturned, the prosecutors have to be losing lots of cases. Otherwise all you can do is keep one individualat a time from being convicted of breaking an unjust or unconstitutional law, which isn't a bad start.
By the same arguement, is it ethical for a judge to give guidelines, disguised as orders to jurors that are unconstitutional? Was it unethical to hide Jews and lie to the government Nazis? Was it unethical to hide Slaves, in violation of the law? Was it unethical to try the nazis at nurenbeurg even though most of them followed the law completely? etc, etc ad nauseum.
Your question is based upon a false assumption. That assuption is that the motives are to make political statements, which isn't necessarily correct. Mostly, we serve on jurys to be fair "peers", who are empowered to decide whether a person's unalienable rights should be revoked or curtailed because of actions on their behalf, based upon the law of the land. It is only fair that not only should the facts, but also the law should be evaluated in each case. To respond to tyrants who would cull out the knowledgable "peers" for the sake of achieving an agenda is actually worse than a juror who creatively presents his/her best side so that he/she has a chance to be a participant. The juror or grand juror is the last check in the judicial branch and the ultimate litmus for the applicability of law.