Why would that be fair. Do smokers pay the same rates for life insurance as nonsmokers? Gay employees are more likely to have AIDS and other illnesses. They should pay more, not expect everyone else to subsidize them.
The other problem you run into is that lesbian women don't get AIDS and are a lot less likely to have expensive pregnancies. Do they deserve insurance on cost grounds?
And if they did pay more---then would THAT end your objections?