All Christians agree that we are required to disobey laws that require us to sin. Presumably, in disobeying these laws, we are hoping that enough people will disobey them that they are either no longer enforced or that they are changed. This suggests that one of the objectives of this kind of civil disobedience is to change a law (or how it is enforced). This qualifies as a type of political activism -- albeit limited to cases where a law requires us to sin.
But things are rather complicated when we consider when, exactly, it is that a law (or legal/political system) requires us to sin.
For instance, there may be no particular law that requires you to sin, but a system of laws or government that makes you complicit in sin. For example, consider all of the infrastructure, bureaucracies, private corporations, etc., that had to participate in a system that lead to the Holocaust. Many, many people participated in this system. Now, supposing that some of these people had enough knowledge of the nature and ends of this political system, certainly any activities of theirs that constituted a clear, positive contribution to the success of the then-existing fascist, nazi political system would have been evil for them, no? I'm hard-pressed to think that it wouldn't be. So, this may mean that a different kind of civil resistance is required of us. In particular, we aren't just required to disobey evil laws, but we are required to abstain from participation in political systems with sufficiently sinister ends. Practically, this may mean that we would be required to quit certain government or corporate jobs, disregard certain bureaucracies when conducting business, withholding certain taxes, etc., with the aim of bringing down the system.
But things get even more complicated when we consider that we can sin through omission. Suppose, for instance, that we have it in our power to prevent some gross evil but don't. I like the example of a doctor who hears pneumonia in the lungs, yet keeps this a secret and doesn't prescribe the necessary antibiotics to treat it. If the patient dies, the doctor is guilty of murder. Similarly, if a judge is in a position to actively overturn an evil judicial precedent but doesn't, he is guilty of sin. Or if he fails to withhold a marriage license from parties that aren't qualified for marriage, then he sins. A person in Hitler's security detail, e.g., may have had an obligation to take a shot at Hitler when he was vulnerable. So, through omitting to take the shot, he may have sinned. Etc.
The point, here, is simple: If Christians must resist government when government requires them to sin, then the extent of that resistance reaches beyond what most Christians today think of. It isn't just sinful laws that we must resist. It is sinful systems, sinful abstention of opposing evil when it is within your power (and position) to prevent it, and more.