Actually, let me be even clearer. When people say "abiogenesis is not part of the theory of evolution" they do not mean "abiogenesis did not happen" or "abiogenesis probably didn't happen" or "aliens did it." They simply mean exactly what they are saying--that abiogenesis is not a fundamental tenet of the theory of evolution. When pressed, they would probably also admit that any number of other things are not fundamental tenets of the theory of evolution. The theory of gravity? Not a tenet of evolution, not required for bifurcated hierarchies. Brownian motion? Ditto. Conservation of angular momentum? Again, nope. That doesn't mean these things have no impact on evolution, it just means they aren't part of the theory.
In reality, abiogenesis happening here on Earth--by which I mean, life here on Earth not being descended from life that formed outside of Earth--is excessively more likely than any of the alternatives. Scientists have many, many falsifiable theories left to rule out before they will ever have to posit anything but Earthly abiogenesis. Not because the alternate theories are unfalsifiable--necessarily--just because as low as the odds are for many of those theories, they are orders of magnitude more likely than any theory of alien abiogenesis for life on earth, or at least any I have heard thus far that is falsifiable, distinguishable from non-alien theories of abiogenesis, and fits the available data. If you believe you have found one, please let me know.
Until then, or until some earthshattering discovery alters the laws of physics in hitherto unforeseen ways, I will remain comfortable with my assertion that with very high probability, assuming life on Earth originated here on Earth will accurately model reality. I can say that even though I am not strongly confident in any one explanatory theory.