Even if the argument "Occam's Razor says that since reality having only one level is simpler than reality having multiple levels, then the first option is more likely to be true." was valid, there is a problem.
Contrarily to other contexts where Occam's Razor is actually useful, none of these options lead us to anticipate differently under any circumstance, so the rational thing to do here is not to apply Occam's Razor, but to reject the question "Does physical reality have one level or multiple levels?"
Edit: Note that I did not mean to say that you should not apply Occam's Razor at all in this scenario. Perhaps, given the hypothesis that reality has multiple levels, Occam's Razor makes certain phenomena more likely, and observations regarding these phenomena could be used to argue for or against the reductionist thesis. The point is that I cannot find examples of such phenomena, specially if the kind of multiple levels that we are talking about are purely physical.
EDIT: Typos.
I have been reading some of the sequences, and this entry shocked me a lot.
If the reductionist thesis is "we use multi-level models for computational reasons, but physical reality has only a single level", then what kind of evidence could support it against the thesis "we use multi-level models for computational reasons AND physical reality has multiple levels?" (let me call it 'anti-reductionist thesis' regardless of what actual anti-reductionists defend). I just can't think of how the world would be different if physical reality had multiple levels than if it had only one level.
In other words, the reductionist thesis, as it is presented here, does not lead me to anticipate differently than the anti-reductionst thesis. Accepting it just generates a floating belief, and as a result, I reject the reductionist thesis, and you should do the same.
Am I wrong? And why?
Wait. Perhaps one of such predictions would be that we should find universal laws involving higher-level entities, while it seems that at that level, we only find ceteris paribus laws. By contrast, at the lower level, we do find universal laws. This should be evidence in favour of the reductionist thesis.
Which would indicate that I was wrong in my initial claim.