The notion that life on earth was created by other preexisting intelligent life, does not really answer the question of life's origin, does it? It's only kicking the proverbial can further down the road. What about the origin of the preexisting intelligent life that created life on earth? See, we're right back at square one only now we have to explain the origin of the preexisting intelligent life that created life. And if the answer to this is still even earlier preexisting intelligent life then we have to account for this too . . . and on and on ad infinitum. The buck will eventually have to stop at a simple, natural, scientifically plausible explanation for the origin of life. So the intelligent life creating life explanation is ultimately a non-answer.
While it is true that scientists do not know with certainty exactly how life began, there are however, multiple scientifically plausible hypotheses for the origin of life, that do not involve intelligent design of any kind. Put these on one end of a credibility balancing scale and on the other end put the very incredible, unprovable, unprecedented, scientifically implausible idea of a supernatural, eternal, all-powerful, uncreated, intelligent being. Now be honest with yourself: which direction should the credibility balancing scale tilt to? However inconceivable the idea of complex life originating from natural, non-intelligent means may seem to you, you would have to admit (if you really think about it honestly and objectively) that the idea of a supernatural origin is far more inconceivable/incredible.
The truth of the matter is using the supernatural to explain the origin of natural life is very illogical and irrational because the existence and origin of the supernatural begs a far greater explanation than the origin and existence of the natural life that it is being used to explain. By way of illustration, using the existence of a supernatural, uncreated, eternal deity to explain the origin of life is tantamount to a foolish man borrowing 1,000,000 dollars to pay off a 100 dollar debt instead of working overtime to raise the 100 dollars. Scientists are working to raise the proverbial 100 dollars. Theists lazily go into a further debt of 1,000,000 dollars to pay off the 100 dollar debt - all the while telling themselves they're no longer in debt and denying it whenever anyone points to the fact that they're now 1,000,000 dollars in debt. LOL.