Musar על סנהדרין 125:27

And know that the habits of scoffing does not become fixed in a man unless he removes the yoke of Heaven from upon him. Therefore, he must be prepared to accept afflictions with which he may be punished, measure for measure. As it is said, "Now therefore be ye not scoffers, lest your bands be made strong" (Is. 28:22). And the Sages would caution their pupils not to scoff, even thouth it might be by chance, without any previous intent. And on this subject they were required to warn their pupils, for many stumble into this fault of scoffing by chance (Abodah Zarah 18b). Scoffing at those who fulfill the commandments is a thing that comes very close to heresy, and he who does so indicates that he does not believe in the commandments. For if someone should mock at the commands of a king, is his life worth anything? Moreover, one who scoffs also causes others to sin in that they will not observe the commandments for fear of his mockery. But one may mock idolatry (Sanhedrin 63:2), and he also may scoff at those who commit transgressions, in order to withhold them from sin. Then, too, others will not commit sins if people scoff a them for so doing.