Molecular rotations that are triggered by external stimuli make plastic ionic crystals intriguing candidates for piezoelectricity, as the change in dipoles due to rotation could be a significant contribution to the piezoelectricity. Several recent papers on plastic ionic crystals emphasize the potential of this material class for piezoelectricity, but the role of molecular rotation is not well established. . This paper provides computed dielectric constants, elastic moduli, spontaneous polarization, and piezoelectric coefficients of 11 representative plastic ionic crystal ferroelectrics. Comparing the different systems, we identified a high shear compliance, caused by molecular rotation in response to shear strain, as a mechanism that can give high shear piezoelectric response in molecular crystals.