I feel like you're reducing everything to material conditions. Joining a union would (statistically) help me economically but my objections to being in a union again are all moral convictions. Perhaps workers are optimizing for concerns you do not share?

Yes, I am reducing unions to economic concerns, but I should mention that most people's "moral" objection to unions is conditioned by parties whose interest is solely economic. When the Koch foundation buys airtime on news programs (effectively) to spread the idea that unions are evil and striking is immoral, it's not because they actually care about morals, it's because unions shift the economic playing field in a way that they don't like.

Is your moral objection that you're opposed to improved material conditions?

I believe I should follow my word. Striking violates my principles.

Would it be ok if you were upfront about the possibility of striking? That seems like a very achievable adaptation.

I think that would be acceptable to me assuming I had assurances I wouldn't be asked to participate or be represented by union actions that would be violent. No threats, no breaking things, no vandalism, etc.

Strikes are generally non violent, and the majority of times that they become violent, it's instigated by strike breakers hired by the company (including police). There is over a hundred years of history of this - plenty for you to read if you want to learn more.