Thus to depict union membership as protecting workers' ability to avoid taking part in the endorsement of views is nonsensical. It is strictly harder to quit a union than to quit one's job. Because the latter not only involves quitting one's job, but also finding new employment in a different field.
(Did you mean "former"?)
I think you're being more than a little hyperbolic. Unions can't force employers to not hire you if you're not a member (in fact most employers probably would prefer non-union employees because the employees have less negotiating strength).
Not to mention that historically unions have been the catalyst for workers rights legislation (like the 5-day work week, and 9-5 hours, overtime pay, and so on). So even if you aren't a member there are obvious benefits to employees who aren't members of a union (in the long run).
This is not the case. At least, it is allowed in States that have not passed legislation to that effect. Many (usually liberal) States have not done so, as it would weaken the power of unions.
Being able to quit a job over a moral objection is a painted as a luxury to most employees (whether it actually is a luxury or not... I think is less relevant than all the media we're fed reinforcing the fact that having a job is a privilege we're lucky to be allowed)