But Darwinists/Evolutionists accept spontaneous generation as true just the same.
No they don't. It seems you are again approaching science with dogmatic labels, then simply stating as fact your opinion as to what all scientists believe.
"Abiogenesis" is the theory dealing with the arisal of life from non-life ("spontaneous generation" is a different theory and has been falsified). Also, the Theory of Evolution has nothing whatsoever to do with the Theory of Abiogenesis, so whether or not someone supports Evolution says nothing of their beliefs regarding Abiogenesis.
You accept as fact something that has not been proven and by you own standards cannot be proven.
Again, a big fat "NO".
Science deals almost solely with "theory" - "facts" and "truth" and "proven" are terms often misleadingly applied to theories.
So scientists may support a theory or not, or they may feel a specific theory is the best given the evidence. Science proceeds by providing falsifying or confirming evidence to refute or support a theory. In this sense, a theory can never be proven as true - even the theory of gravity, as you example.
Thus, if someone says to you "the Theory of Evolution is true", or "the Theory of Abiogenesis is fact", that person is not a genuine scientist. (And if you have a source telling you that scientists claim these things, it is probably Creationist propaganda...)