One cannot assume a negative. Much as one cannot prove a negative. By virtue of the scientific method, the one making the assertion carries the burden of proof.
I more or less agree. However, before proof,
all is negative.
So, abiogenesis is life from lifelessness. This is the observation to justify that: we exist, as do gazillions of other life forms, and direct and indirect evidence that the current state of life on Earth is about 1% of all life that's ever been on Earth. From that, hypothesis have to be made as to how life came from lifelessness.
Suppose certain chemical elements came together in just the right fashion, at just the right time, with just the right energy influence, etc., etc. This is one supposition, completely unsupported by any fact, any proof, any empiracal data, anything at all. But, it's considered a scientific supposition.
Now suppose that an intelligence beyond our four dimensions put those chemical elements together in just the right fashion, at just the right time....... This is a supposition completely unsupported by any fact, any proof, any empiraclal data, anything at all. But, it's considered a non-scientific supposition. Why? In the randomness of all the universe, if we can create new laws when we can witness things on the subatomic level that don't follow current laws and when we can presume the first 10E-43 seconds of universal existance can have different than our currently understood natural laws, why can't we accept yet another possibility of different natural laws (a supernatural entity)? It's just a supposition, with the same facts supporting it - we exist.
We don't know the conditions under which life first came from lifelessness. Any test we would perform would be tainted by our very existance into that test - contaminating the lifelessness from which we would be testing life. It's pure fiction to imagine any test that could reasonably prove any theory. Because we cannot show any reasonable explaination of life from lifelessness, the mere concept would have to ALSO be considered supernatural. Does that mean we no longer exist?
I cannot prove that an invisible weightless unicorn is not taking a dump on your head right now. You can't prove it either - however if I were to insist that there was one, you may politely disagree, but inside you'd think I was a damn fool.
Science does not assume that God did not create the universe. It merely states that there is no proof that He did, and therefore no theorums may rely on the assumption that He did.
One difference. You don't prove a negative. Saying "There is no intelligent design" is not an affirmative sentence, and therefore does not require affirmation.
There's no observation of the unicorn. There is an observation of life.
George Carlin did a line in one of his appearances on Carson (with Flip Wilson, they were newsmen and it was hillarious ((mostly))), where he said that a new disease was discovered. It has no symptoms, does not effect the body in any way, has no known cause, and no known cure. I think it's the unicorn!
I agree science cannot assume there's a God. But, when brainstorming the initiating factor of the universe, or of life itself, it's idiotic to rule out any potential answer when no answer without it comes any closer than an Intelligent Designer. I don't seek everyone to agree that there's a Creator, just don't dismiss one of the potential answers, and claim it's not science to think beyond our four dimensions.