I've spoken out in the past when I felt that my employer's internal policies were not acceptable. In my case it was a harassment issue and once I took a moral stand on the topic, the behavior stopped, my firm rolled out a handbook supporting EEOC guidelines, and others within my group thanked me for saying something. When you take a moral stand on a matter it often empowers others.

You have the right to share your opinion and to pass up the project if you no longer choose to tolerate the situation. Express that participating in weight discrimination when reviewing potential candidates is not congruent with your personal ethics.

As far as the "party line" that your boss gave you for not being able to afford health insurance, I would assume that there is no evidence to support this reasoning. The applicant may not require any extensive medical coverage.

Interestingly, there was a recent study that showed that more than half of overweight people are actually perfectly healthy, and a similar number of skinny people may be unhealthy/

Your firm is not the only company participating in this behavior. According to the International Journal of Obesity, weight discrimination "occurs in employment settings and daily interpersonal relationships virtually as often as race discrimination, and in some cases even more frequently than age or gender discrimination." As there are no federal laws that prohibit this type of discrimination, your boss and managers' behavior may continue.

If you do not stand by your company's standards, you might look to align yourself with another institution. Your firm's reputation is its greatest asset, and being an employee there, you represent their values. Perhaps you might want to consider pledging to a workplace where you feel proud to be a member.