This question asks why anti Polygamy laws exist.
Marriage require consent of 3 parties. The man, the wife, and government.
If Ann is married to Bob, then it must be registered in government database. If Ann then want to marry Charlie, then why can't government simply make that impossible?
Before marrying anyone, government can simply says, ups, you cannot marry, you are still married based on my database.
Rather than punishing polygamy, why doesn't US government simply make that impossible by not officiating marriage between people that are not single?
Why punish something you can effectively prevent people from doing in the first place easily?
Note: This question has many good answers. I was just pointing out that I was under the impressions that polygamy can only be done by mistakes. Why would anyone commit a crime with almost 100% probability of getting caught. In game theory, it's not "reasonable" (or what's term in game theory for picking a strategy that is strictly dominated no matter what).
I think anti polygamy laws is a bit similar like https://www.news.com.au/travel/travel-updates/woman-forced-to-cancel-dream-trip-to-new-york-after-accidentally-telling-the-us-shes-a-terrorist/news-story/bc496a06a6ae8891853c0df19a06d4e1 You will be in trouble for checking yes I am a terrorist but that's pretty pointless. Why would anyone do that?
Another issue is that polyamory and sugar relationship is legal in United States. So why would anyone that want to have several woman just don't involve the state.
Hence, committing "legally recognized" polygamy, in a sense of registering your second marriage is a crime with 100% chance of getting caught and with almost nothing to gain. Doesn't seem like something need criminalizing. No body would bother doing that anyway.
Also I think this is still a legitimate question. That is why I am reopening.