Marauders are raiders that look to take other people's supplies for their own gain. Depending on the SHTF situation, these individuals may pose the biggest threat of them all. In the case of long-term power outages, or societal collapse the presence of marauders will be amplified. The reality is that most people are not prepared, so when supplies run low and times get desperate, ugliness will present itself. One would like to hope that in emergencies and post disaster scenarios, that the community would support each other, but the reality is that when you have supplies and other don't, you can expect people to come for them.
While some marauders could generally be decent people who are just desperate to provide for their families, you can assume that marauders will be made up of a criminal element with bad intentions. The worst marauders won't stop at stealing supplies, they are willing to and perhaps planning to cause harm. Even good-natured people will go to unimaginable lengths to provide for their loved ones when desperation occurs.
Believe it or not, there are preppers that are not necessarily gun advocates; but once you start planning for worse case scenarios and the thought of marauders becomes a focus it is hard to think you can protect your family and supplies without firearms. There are obviously, other ways to protect yourself, like fortification, but that will only provide protection for so long. Additionally, you may not encounter a marauder on your property where you may have the advantage. If you need to venture out for supplies during a social breakdown situation, you may need to fight to protect yourself and any accumulated supplies.
For those of us that watch "The Walking Dead", it becomes clear that in a social breakdown scenario, the real threat is other people. But you don't have to find yourself in a zombie apocalypse or a "Mad Max" movie to encounter marauders, they will appear as soon as supplies run low, or criminals feel they can get away with taking advantage of the chaos.