You can frame it that way, but then you’re just adding more independent agents into the mix, attenuating the causation even further.
You’re now saying it’s a sin to not act to help prevent another from compelling you to provide the means of committing sin to another adult.
Again, I wouldn’t be completely shocked to learn that that is standard Catholic teaching about sin, agency, and causation. But it would be nice to see some evidence of that which pre-dates the current contratemps – and even better, application of that principle to something other than women’s sex lives.
This is true for people who buy their insurance as individuals on the open market on their own, where they carry 100% of the cost. Your employer has negotiated with the insurer they use to get Coverage X for their employees for Cost Y. And they’re paying for a large portion of it.
As far as the salary you negotiated by taking health care costs off the table, your point would be better made if while being employed at the same job, where your employer is paying $700 per month on your behalf, you talked your employer into give you an $8,400 annual raise for you dropping your insurance.