The algorithm-structure interaction hypothesis is contradicted by the fact that US-specific experiments directly testing algorithmic effects in the US political context also find null effects on affective polarization.

[DEFENSE-REBUT → q9b5z1] Guess et al. (2023) tested algorithmic feed effects on US users during the 2020 US election and found no significant effect on affective polarization despite substantial changes in content exposure. Gauthier et al. (2026) tested X's algorithmic feed on US users and found no significant effect on affective polarization, providing a US-specific test on a second major platform. If algorithmic effects were uniquely amplified by US political structure, experiments conducted in the US context should detect these interaction effects, yet they consistently find nulls on affective polarization. Therefore, The algorithm-structure interaction hypothesis is contradicted by the fact that US-specific experiments directly testing algorithmic effects in the US political context also find null effects on affective polarization. (Warrant: An interaction hypothesis predicting uniquely large US algorithmic effects is disconfirmed when US-specific experiments testing those exact effects find null results.)

• Guess et al. (2023) tested algorithmic feed effects on US users during the 2020 US election and found no significant effect on affective polarization despite substantial changes in content exposure.
• Gauthier et al. (2026) tested X's algorithmic feed on US users and found no significant effect on affective polarization, providing a US-specific test on a second major platform.
• If algorithmic effects were uniquely amplified by US political structure, experiments conducted in the US context should detect these interaction effects, yet they consistently find nulls on affective polarization.

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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