If you carry OC and a pistol, and use your pistol, what legal argument have you opened up against you?
None. On a use of force scale OC is near the bottom and not an appropriate response to a DEADLY threat.
Most people think of the use of force scale as a ladder you must climb, using every step along the way before using deadly force. This is just not true.
I prefer to teach the use of force scale as an elevator. Go to the appropriate floor for the situation.
As an example...every LEO in the US is equipped with some level of less lethal force (OC, Baton, TASER,etc). They do NOT need to attempt to use these when facing a deadly threat. Those items give them options for dealing with a problem that does not rise to the level of DEADLY
The same holds true for the cilivian defensive encounter. The fact you have OC, does not make it the correct choice against a deadly threat.
I carry a small can of OC with me all the time. Its for occasions where my pistol is NOT the correct tool, but i need something besides my hands.
A good example is an AGGRESSIVE begger, someone who is threatening your safety, but not visibly armed. In a situation where you cant just move away and he is closing the distance (empty handed) after being told to go away (verbal commands are part of that use of force continuum).
Hand on with a "street person" is NASTY. Lots of health reasons to avoid that. If possible. A quick blast of OC into his/her face is likely to make them change their mind about continuing the aggressive behavior. It may not, and you need to be prepared for that as well, but its worth a try.
As an OC Instructor, i feel the need to add, its not 100%...nothing is. It also has some limiting factors that must be included in the deployment thought process. Wind is the biggest. All that said, its an OPTION that allows me greater flexibility in my response to a threat.
Does not mean i MUST use it, but i can if its appropriate.
Edit to add: With ANY cilivian use of force, it needs to have a police response for follow up and reporting. Dont just spray and head for home. Call 911, inform them of the incident and have a report taken. Just CYA