It's really more of a matter for /k/, but first off, how certain are you that you won't be able to get a real gun?
As a European gun owner, I didn't find it particularly difficult to get a permit for hunting. A bit expensive, perhaps, but nothing too bad.
If you really cared about protecting your life with a gun, it stands to perfect reason that you'd do what's possible to get one, right? Now, even if you were to think yourself above hunting, chances are that practical shooting or western shooting federations are in place and recognised in your country. Join them for practice a couple of times, and you'll likely find yourself owning a gun within months.
I don't mean to sound condecending to any Yanks who might take offense, but gun ownership in Europe is a bit different from what you see on /k/; you're kinda expected to use your gun for something, maybe together with others, instead of shitposting about it and your plate carrier and going innawoods to fight black people/yellow people/Hillary/Trump/skinwalkers/the patriarchy... One isn't more right than the other, but the laws have been written around those cultural norms, and unless you can change it, work with what you got.
Second, provided you for whatever reason cannot get a real gun, are there unregulated alternatives available in your country? Bows, crossbows, spearguns? Either of those will be a fucksight more lethal than a regular airgun.
Third and last, NO, a regular air gun will NOT be something you want to use to save your life from someone who's desperate enough to assault you in your own home.
If you're getting burgled, chances are it'll happen while you're out of the house - Lower risk for everyone that way.
If someone breaks into your house and doesn't fuck off when you make your presence known (and you're not an ancient cat lady they can hush down), chances are they're not going to be deterred by what's basically a hopped-up airsoft gun.
