Since it is the pathway used in even the simplest of cells as far back as we can ascertain, it is a conclusion warranted on the evidence.
That is not necessarily the case and indicates, as you have mentioned, that certain organics found in the complicated metabolic paths of even simple cellular organisms present today could not have existed during biogenesis. This is also a clear indication that whatever the first life forms were, they are not comparable to today's cellular life forms.
This is a circular argument: Abiogeneis didn't create cellular metaoblism because cellular metabolism cannot be formed by abiogenesis. You're caught in the circle because you are treating the premise as fact. That's a no-no.
Again, that is an assumption. We don't know if the first living things were even cellular like what we see today. The simplest things have had competitive pressure for billions of years. We don't know what the earlist life was like so to assume current metabolic pathways today are the sam as in the past is an assumption.
This is a circular argument: Abiogeneis didn't create cellular metaoblism because cellular metabolism cannot be formed by abiogenesis. You're caught in the circle because you are treating the premise as fact. That's a no-no.
You have assumed it is a circular arguement. You have failed to consider that the pathways(s) involved in abiogenesis must be equivalent to what we see today. There may well be an initiation mechansim that is unknown to us at this time. A simple chemical analogy would be free readical polymerization. THe same monomer units are used to build the chain of the polymer. In your logic, these must be the same chemical units used to initiate the process. In fact, separate chemical initiators are used to start the process, but once started, it continues without the need or initiator. The initial state is not the equillibrium state. It is reasonable to suspect this is the case with abiogenesis.
You know that the Krebs cycle doesn't exist in anaerobic bacteria, which are some of the simplest currently existing organisms. The Krebs cycle only operates in aerobic organisms. Anaerobic organisms derive energy exclusively from glycolysis.