Why is it a good idea to put some salt in the bread dough?
Common table salt is not necessarily an antiseptic in the conventional "sterilizing" sense. What gives it weakly antiseptic properties in biological context is its ability to absorb water from cells through osmosis, should the concentration of the salt outside the cell be too high, the cell would lose too much water through its membrane and die.

However this is strongly dependent on concentration. For example, according to this source, a concentration upwards of 20% is required to kill bacteria; at lower concentrations the salt will only hinder growth, which is most likely the reason it is added (in moderation) to bread.