You are incorrect that strikes are unethical. This isn’t something that’s controversial. The employment relationship is that capital/management provides wages to labor, and labor provides their, uh, labor. When labor decides that they aren’t getting an appropriate deal, they will stop providing their services and, in return, management stops providing wages. Nobody’s held hostage – management has the legal right to hire scabs; if they don’t do this it’s because they believe their business is better served by other actions.
Note also that there’s no lack of mutuality – management has the power to send people off on furloughs at any time, and they sometimes do. The reason it doesn’t happen all that often is that management is typically already getting what they consider a good deal from the wages for labor transaction – businesses don’t employ more people or more highly compensated people than they absolutely have to to generate profit; if they figure out a way to make their widget more cheaply, they just lay those people off. Why is it that management id (again, typically) so much more satisfied with their end of the deal than labor is? Is it because labor is antsy or flibberdigibbet? No, it’s because management has much, much more bargaining power and, so can set terms that aren’t fair but will still attract employees.
Finding strikes unethical is the same muddled thinking that says that it’s immoral to stop paying your mortgage on an underwater house (efficient breach – it’s cheaper to pay the penalty for breaking a contract than for performing), while businesses cause efficient breaches all the time and, in fact, management can be sued by stockholders by failing to so so in extreme circumstances. The other side sees your interactions in terms of dollars and cents – by refusing to see it the same way, all you’re doing is making it easier for them to screw you.
Anyway, your options as presented appear to be laboring under a different misapprehension. Assuming you’re in the U.S., if your job is covered by a union with a collective bargaining agreement, most likely you’re already receiving most of the benefits of the union’s work. I won’t say it’s unethical not to join – you have a legal right to stay away. But the fact that you’re wary of strikes shouldn’t be the ethical touchstone given that – in most situations – you’re already likely freeloading on union members.
One final point – if you’re afraid of being an object of derision as a union member who crosses the picket line, I wouldn’t worry. The derision will be about the same for any scab, whether he’s in the union or not.