That was a strange emo episode. Would have made somewhat more sense if Touma had suggested he will help Railgun to stop Accelelator. A kind of a strange approach to simply try to make her dream crumble without any option offered instead. Although not necessarily a bad one as such. Basically he was forcing Mikoto to rethink the decision and her own values. Not a very effective solution and quite a painful one no doubt (for both of them) but perhaps it will open a road to a more lasting change of thinking.