There's a difference between believing that the nation's laws, properly interpreted, don't give the government jurisdiction and expecting the government will abide by that claim. We can see the difference more clearly by looking at countries, such as Russia, which have paper guarantees of civil liberties but shouldn't fool anyone into thinking it's safe to exercise them. Defending oneself in court may be futile under those circumstances, but ignoring the summons (assuming they aren't already in detention) without going into hiding would be more foolish. Also, appearing in court gives them a chance to state their arguments publicly. Going to court is both the more principled and more sensible thing to do.

You can argue that the people claiming they have the right to criticize Putin are right, and the ones who (for example) say that income tax is optional are wrong. But given their views, going to court to argue them is the right thing.