The reality is that rioters seeing armed security at a business or residence are likely to head somewhere where the looting and destruction is much easier.
Note that I am differentiating armed security from right-wing militias The right-wing militia people will be out on the street and are many times intent on starting a conflict. We will continue to see the ANTIFA versus right-wing militia conflicts (and idiocy) play out in the streets.
Most armed security employees simply want to get home to their families later -- but they will take action within the law to use deadly force to defend the property they were hired to protect. They are not just going to stand-by and not use force when looters crash the building.
If ANTIFA and other want to escalate their violence after the election then you are right -- the shiat is really going to hit the fan when they run into paid armed security. But I bet they don't attempt to cause trouble with them a second time -- once the lesson is applied the first time.
Business owners are increasing hiring armed security. In Raleigh after downtown business owners were looted and burned out a second time -- their local business association started urging them to hire private armed security and provided a list of reputable firms who provide these services. I will note that not a single business that hired armed security in downtown Raleigh has been looted or burned by our local ANTIFA groups (e.g. BURN Durham, etc.) since they have been present. In fact ANTIFA now seems to be scared of going anywhere near these businesses -- and confines their activities to the Wake courthouse and government building area.
It depends.
It depends on the suspects. Some may be looking to attack security. Cops get killed. People willing to kill cops aren't afraid of security.
Cops get attacked in riots. People willing to attack cops in riots, won't be deterred by security.
I agree with @CaptainObvious that most sane security guards aren't looking to be the subject of more riots and news broadcasts. They will shoot as a very last resort to save their own lives ... not to save property, etc. How much are they getting paid?
The U.S. really needs to stop pretending that there is no excessive-force policing problem in this country, because I doubt this won't escalate beyond bricks, mace and Molotov cocktails...especially if the election goes "badly." (And I'm not just referring to a knee-jerk reaction.)
It takes the whole village to end the madness.