I had a gbs + swab with my first pregnancy, decided after much deliberation that I would not have IV abx. Did deliver in hospital though just in case. The fact that many women have it and don't know about it but end up being fine, plus the fact that there are serious risks associated with having IVabx were the deciding factors for me.
My consultant was not even happy for me to have IV abx in a midiwfery led unit close to the main hospital in case of a reaction. Your risk of a mild reaction is 1 :1000, a severe reaction 1 :10,000 and a fatal reaction 1 :100,000. The risk of a term otherwise healthy baby dying from gbs is slightly higher than the risk of having a severe reaction to antibiotics. If you have a severe reaction to antibiotics, your baby might well die or be brain damaged anyway.
My personal opinion after finding out all of these statistics was to not go for it, but women have to make their own informed decisions about it, as their labour may not progress if they are worried about some aspect of it, such as that they wish they had stayed at home, or that they wish they had gone in for abx.
Anyway everything was fine with me, went on to have a homebirth second time round not even considering having abx. Had there been any probs at all or had I been less than 37 weeks, then I would have gone for them though.