Are defensive votes worth defending? The answer depends on your principles and objectives.
The concept of state abolition relies on the moral principles of individualism and liberty. The state acts contrary to these principles. Participating in state processes can give it de facto legitimacy, a false sense of its value in a given society, and the notion of accomplishment by voters when their preferred candidates win an election.
If potential participants are under the illusion that their actions will achieve their desired outcomes more often than not, then they may be convinced to regularly participate. If they hold no such illusions, then they are likely to not engage.
Is there a middle ground? Should one engage the system while knowing that their desired outcome is not likely? Opinions on engagement and defensive voting vary among those advocating for a stateless society.
Some contemporary advocates of anarchism, such as CrimethInc. and Larken Rose, say that it's immoral and useless to vote at all. Their reasoning follows in the tradition of Bakunin, Kropotkin, and Thoreau - that the state, and voting in general - is a fraud and an evil perpetrated on society.
On the other hand, Proudhon, Spooner, and contemporaries like Zinn and Chomsky believed that voting - and even running for elected office itself, in the case of Proudhon - was a valid action on the road to anarchism. Spooner pointed out that even abstaining from voting had been argued as giving legitimacy to the state.
From a moral perspective one can argue that the state is illegitimate force, therefore, participating in it, especially voting for your preferred agent of force, is morally wrong. But from a practical perspective, defensive voting can occasionally yield positive results. Sometimes, practicality is needed more than rigid ideology.
The notion that a stateless society can be achieved in a short time frame (such as a generation) is almost absurd. Persuading the average person to even think about such a society is nearly impossible. Persuading them to think about it and the perils of current society critically, even more so. This leaves advocates of state abolition in a position where efforts to achieve our philosophical goals run smack into the much greater effort to suppress physical liberties at the hands of the coercive and well-funded state machinery.
To put it another way: Talking without walking is not likely to get you to your destination.
Yes, it's true that the state, without the consent of the governed, is illegitimate. Yes, any candidate that wants to use the illegitimate state as a means to deprive others of their liberties is immoral. Yes, voting your way to anarchism is almost completely unlikely to occur. These are truths that we accept as state abolitionists.
Sometimes condemnation and abstention isn't enough. Does this mean that the aforementioned truths should be ignored or discarded as part of the philosophy? Not at all. But they should not prevent actions that may have an actual impact on individual freedoms.
Knowing that the state will invariably continue down the same path to more authoritarian rule and knowing that it is in fact immoral and illegitimate, one can still attempt to mitigate the damage that it does along the way. When given choices, as awful as they may seem to an anarchist, there can be options available that are worthy of support. There may even be candidates or referenda that explicitly move the needle in the opposite direction, even if temporarily.
That is not to say that these choices come along frequently and participation in state processes should be routine. It is actually a rare occasion that laws and lawmakers return liberty to those that have been deprived of it. But when the opportunity presents itself, it would not be wrong to seize it and use it to one's advantage, while still advocating for and working toward the ultimate goal.
There is a time and a place for defensive voting. Those times and places are up to those making their own moral and philosophical decisions. As long as your participation falls in line with your underlying principles for individual freedoms, voting in order to reasonably restore or protect those freedoms is a principled decision.
Keep in mind that the alternative to never participating is to leave your future livelihood entirely in the hands of those who believe the state's force is legitimate and necessary. Defending yourself from those votes is only possible if those votes can be countered. Attempting to head off new or worse violations of liberties is preferable to trying to reclaim them once they've been stolen.
One can choose to fight defensive battles without going to war.
When given the option to support a candidate or law that explicitly fights encroachments of or restores liberties, it would be acceptable from both a moral and a practical perspective to vote for that candidate or law. At the same time, it is necessary to explain why the candidate or law is preferred and continue to advocate for increased liberty, with the long-term goal of abolishing the state. These defensive voting opportunities may be few and far between but they can certainly be part of an effective strategy on the road to state abolition.
Use your individual moral judgement to the best of your ability when making a decision to vote defensively or not at all.