A dilemma for thought experimenters

Thought experiments do not have a life of their own ... because of the following dilemma. We either have experience with a situation that is relevant to the thought experimental situation or we don’t. If we do, then our thought experiment just tells us what we know from concrete experiments (or observations). But if [we] don’t, then the thought experimental result amounts to mere guesswork.

Sure, but it depends on what you mean by "guesswork". In a sense, if it means "not being based on direct or reported experience", then yes. Now, many other forms of whatever you might think of as evidence (arguments, for instance) will be guesswork just as much. If, however, "guesswork" means "random conclusions that draw upon intuition" then sure again, but then we're agreeing to a rather different conclusion, for the suggestion is that the outcome is irrational. One way out of this dilemma was famously supported by Norton (1996), who recognizes the split in the road but saw a way out.

Norton, J. (1996). Are thought experiments just what you always thought? Canadian Journal of Philosophy, 26(3), 333–366.

Reiss, J. (2002). Causal inference in the abstract or seven myths about thought experiments. Technical Report CTR 03/02, Centre for Philosophy of Natural and Social Science, London School of Economics, London, UK