Not a fan of Boeing, but doesn't it make sense to not pay for the health insurance of employees refusing to work?
If they are not fulfilling their obligations, why should Boeing fulfill theirs?
But to your specific point, yes, it makes sense for them to use worker's healthcare needs to attempt to force them to concede, from a cold game theory perspective. I hope folks will see workers in the same light if workers are able to find additional corporate weaknesses to exploit. Boeing is losing $100M-$150M/day until the strike abates and an agreement is reached.
https://news.ycombinator.com/item?id=41720658 ("HN: Why is US health care like this?")
(The purpose of a system is what it does)
Sure, but salary is also used to control workers - striking workers don't get paid, either. They probably don't get employer contributions to their 401k.
They aren't getting Social Security contributions during the strike, either.