Nothing for the most part is illegal to use in self defense if your life is in danger. The trick is not to carry it for that intended purpose.
Correct, but (at least in Texas, which is the only set of laws I've reviewed for this purpose, so YMMV) the use of wasp spray to the eyes could (COULD, I know of no caselaw) be considered Deadly Force due to the risk of Serious Bodily Injury, which can put it (legally) on the same level as a firearm.
It's a case where the method of employment is as important as the weapon itself. Shooting and stabbing and always considered Deadly Force afaik. With other weapons (blunt force weapons spring immediately to mind), the location of the strike is what makes the difference. A baton strike to the leg or forearm is lessor use of force than the same strike, with the same weapon, aimed (or landed) on the head/neck.
Wasp spray to the eyes has every potential of causing significant permanent damage to the recipient, so I wouldn't be surprised if such a use were ruled Deadly Force.
As far as the general topic of Sketchy People and Sketchy Situations: I've camped in front country, back country, etc. for years, and I've spent about 10 years as a LEO in state parks. I've learned that good situational awareness is the best protection you can have. The best resolution is to avoid the problem in the first place. If that means to have to choose another campsite at 2:00 am, so be it.
But some people cannot be avoided. I say "people" because 99% of the situations will involve people rather than wildlife. If you choose to be friendly and nonthreatening that's perfectly fine, though I really don't think it's 100% effective. I've absolutely seen people talk their way into getting harassed, threatened, and robbed by the homeless guy who's just friendly and talkative and bad with social cues until the drugs wear off. I will say that there's a big difference between appearing nonthreatening, and being incapable of causing harm. "Be Professional, be polite, but have a plan to kill everyone you meet" is a bit of an oversimplification, but it is important to be able to recognize when nonthreatening isn't working and it's time to play an more active role in your immediate self-protection. How you choose to play that role, and the tools you decide to use to do it are up to you.