The algorithm-structure interaction hypothesis is contradicted by null results from experiments conducted within the US political context that should capture any such interaction effects.

[DEFENSE-REBUT → sp3svx] Guess et al. (2023) and Nyhan et al. (2023) tested algorithmic effects on US users during the US election, the context where algorithm-structure interactions should be strongest, yet found null effects on affective polarization. Gauthier et al. (2026) tested X's algorithmic feed on US users and found no significant effect on affective polarization despite the US two-party context. González-Bailón et al. (2023) documented asymmetric ideological segregation on Facebook, but descriptive segregation patterns do not establish that this segregation causes affective polarization at the 10 percent threshold. Therefore, The algorithm-structure interaction hypothesis is contradicted by null results from experiments conducted within the US political context that should capture any such interaction effects. (Warrant: If US political structure amplifies algorithmic polarization effects, US-specific experiments should detect those amplified effects, yet they consistently find nulls.)

• Guess et al. (2023) and Nyhan et al. (2023) tested algorithmic effects on US users during the US election, the context where algorithm-structure interactions should be strongest, yet found null effects on affective polarization.
• Gauthier et al. (2026) tested X's algorithmic feed on US users and found no significant effect on affective polarization despite the US two-party context.
• González-Bailón et al. (2023) documented asymmetric ideological segregation on Facebook, but descriptive segregation patterns do not establish that this segregation causes affective polarization at the 10 percent threshold.

These are challenges this argument’s reasoning pattern must still withstand. Answering them on Isonomia strengthens the argument.

• Could a different cause produce the same effect E in this case?Open
• Is there a plausible causal mechanism by which C could bring about E?Open
• How strong is the causal generalization linking C to E? Are there documented cases where C does not produce E?Open
• Are there intervening or confounding factors that could interfere with the causal chain from C to E?Open
• Is the apparent link between C and E merely a post hoc correlation rather than a causal relation?Open

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