We conducted a randomized survey with 2,666 US residents to study preferences for legalizing payments to kidney donors. We found strong polarization, with many participants supporting or opposing payments regardless of potential transplant gains. However, about 18 percent of respondents would switch to favoring payments for sufficiently large increases in transplants. Preferences for compensation have strong moral foundations; participants especially reject direct payments by patients, which they find would violate principles of fairness. We corroborate the interpretation of our findings with a choice experiment of a costly decision to donate money to a foundation that supports donor compensation.