oomis1105-
I agree that people should be allowed to know their status if they desire but keep in mind that Dor Yeshorim is subsidized and this is how they decided to run it. As far as they are concerned- you can go to a lab (pay full price) and asked to be tested for whatever genetic disease you would like to know the status of.
I know of a large family where the two parents got tested by a lab and got the results. They found this cheaper than each of their 10 kids getting tested through Dor Yeshorim.
Who ever runs it feels that there are reasons why it is better for one not to know their status that outweigh the reasons to know it. One obvious reason is the stigma that will be associated with any person/ family that is a carrier. (One rumor I heard is that if a couple both know they are carriers, get married anyways and R”L have a child with the genetic disease, the insurance company can claim it was a pre-existing condition.)
If a potential couple is found to be incompatible they are notified as to which disease they are both carriers of. The reason being is that there is a false positive result in a small percentage of cases (4% in the case I am familiar with) and the potential couple can go for genetic counseling and have more expensive tests done ($500 each in that instance) that have a much higher accuracy rate.