Wolf has a recent discussion on his blog about the pros and cons about giving Orthodox marriages for otherwise unOrthodox couples for fear of creating mamzerim.
Ok, that's fine and all and I can understand why you'd want to avoid having more mamzerim around if you hold by the laws stringently. As far as anyone knows, most people are not mamzerim and a mamzer can only marry other mamzerim (or converts). It leaves quite a stigma which never goes away. No matter how far the initial mamzer's line descends. His lineage will forever be one of mamzerim.
However, let's look at this more closely. What is the only real difference between a mamzer and a non-mamzer? The only real difference is this social stigma and the limitations on who the individual can marry. The only reason one would not want to be a mamzer is because one'll be looked down on by all the non-mamzerim and will be limited in marriage choices.
Wouldn't the social situation be so much better if _everyone_ were mamzerim. Then there would be no "untouchable" nebuch class in Judaism and there would be no marriage restrictions (beyond the other regular stuff). And one a mamzer, always a mamzer, so there would be no way to turn back into "regular" Israelite.
I say we should just assume we are all mamzerim and not worry about it. What's the worst that could happen? We could marry a mamzer and our kids could really be mamzerim? Oh no, that's exactly the same.
Just so y'all know, I'm not a mamzer, but I do work for the Free the Mamzer Foundation. Check us out at FMF.org