Argumentation schema theory guided four experiments on the processing of plausible and implausible reasons and warrant statements testing the hypothesis that most reasons produce greater agreement with claims than when claims are presented without support. Another hypothesis was that leaving warrants unstated often produces greater agreement than when the warrant is made explicit. In Study 1, American participants were more likely to agree with claims after they read arguments than beforehand--even those with implausible reasons and warrants. In Study 2, American history and environmental science majors read brief arguments and agreed more with implausible arguments than claims alone. Study 3, with Chinese participants, replicated some but not all earlier results. In Study 4, with Chinese participants, blatantly false claims supported by bogus reasons yielded marginally greater agreement than unsupported claims. These findings suggest that many people have uncritical argumentation schemata with low support thresholds, making them vulnerable to weak and bogus arguments.