I saw an academic study where they estimated that something like 1/4 of marriages in the ptolemaic period of ancient Egypt were brother sister marriages. I think it was very common throughout ancient Egyptian history and was repeated over many generations. This is the longest civilization in human history. I think people wildly exaggerate the overall detrimental effects of inbreeding partly because the potential consequences can be literally life and death. Also there's the reality behind all taboos- tapping into non-rational emotions of fear, disgust and ecetera is very effective in discourages the behavior and almost completely shuts off any other possibilities. The largely irrational taboo has an overall positive effect by discouraging inbreeding but like all taboos it comes at a cost- a cost people in your situation feel most acutely.

I'm kind of disappointed with many of the responses here that dismiss the stigma surrounding your situation- I'm sure the implied rejection you have felt has been pretty extreme- not to mention some direct rejection. Posters here are just ignorant of how it feels to be degraded by society in that way. Some here do raise a good point about people largely not caring and being too selfish to care that much- it's true most people just don't care that much. Even when they are mocking and negative it's usually just salacious gossip to them- they actually don't care that much even when it seems they do. It's just entertainment for them. For you it probably obsesses and devastates you, for them they won't think about it again in couple of weeks. Sure you know it already but there's no need to share anything about with the vast majority of people out there and it's probably for the best given their mentality. You don't owe them anything. If its a person you know and trust and who's open minded, can be good to share and educate them, everyone else it's not worth it. If they don't know you well enough they will just label you. Their bias is largely irrational and very deep rooted. Who needs that stigma? The most rational and eloquent argument will only shift their perspective a bit, while you have to bear the burden of the stigma. IMO it's really not worth it in most cases.

As cliche as it sounds, if you can learn to deal with this and not let it poison how you feel about people, you reallly will be a stronger better person than most. Keep your head up.