As for logic vs the Bible, to the non-believer logic trumps the Bible. The believer uses logic but starts from an assumption that the Bible contains the Word of God and thus limits logic: Reason is subservient to Divine Revelation. The non-believer does not accept that premise. The argument will quickly devolve into a debate about the authority of Scripture.
Yes, these posts quickly become polemics and opportunities to hurl contumelies. The very first response the original poster received was someone telling him that his God was a demon. I agree that we should keep our dialogue respectful, but that goes both ways. Deliberate misrepresentations of each other's positions does not add to the debate.
As for why Calvinists hang out at freerepublic.com, my guess is that it's because there is a long tradition of industrious free enterprise among Calvinists. The term 'Puritan work ethic' is sometimes used to describe this correlation.