People have different notions of what constitutes their space, and sometimes there's overlap, so problems ensue. Take for example the issue of abortion. If I were a female who was heavy with unwanted child, I would argue that I do not believe that a fetus constitutes a human being, and the entity is within the domain of my own body, so I should decide whether or not to extract it. The pro-lifers would say that because I live in a society, I have given up some personal freedoms in order to protect myself and the other constituents of said society. One of those freedoms I have given up is the ability to kill people who are weaker than me. The pro-lifers believe that allowing me the freedom to extract a fetus is no better than allowing me the freedom to murder a homeless man. Being a society, we cannot and should not allow this behavior.
Because there can be no agreement as to who is right in this case, no matter the outcome, somebody will feel stepped on. Those who are stepped on will not get along with those who stepped on them, for the same reason you don't tolerate the burglar who pilfers your copy of Super Smash Brothers.