Quote 13
At that time my virtue slumbered; my evil, kept awake by ambition, was alert and swift to seize the occasion; and the thing that was projected was Edward Hyde. (10.8)
For Jekyll, repressing his evil side simply renders it more ambitious and alert.
Quote 14
The pleasures which I made haste to seek in my disguise were, as I have said, undignified; I would scarce use a harder term. But in the hands of Edward Hyde, they soon began to turn toward the monstrous. When I would come back from these excursions, I was often plunged into a kind of wonder at my vicarious depravity. This familiar that I called out of my own soul, and sent forth alone to do his good pleasure, was a being inherently malign and villainous; his every act and thought centered on self; drinking pleasure with bestial avidity from any degree of torture to another; relentless like a man of stone. Henry Jekyll stood at times aghast before the acts of Edward Hyde; but the situation was apart from ordinary laws, and insidiously relaxed the grasp of conscience. It was Hyde, after all, and Hyde alone, that was guilty. Jekyll was no worse; he woke again to his good qualities seemingly unimpaired; he would even make haste, where it was possible, to undo the evil done by Hyde. And thus his conscience slumbered. (10.11)
Dr. Jekyll represses any ticklings of his conscience.
Quote 15
But time began at last to obliterate the freshness of my alarm; the praises of conscience began to grow into a thing of course; I began to be tortured with throes and longings, as of Hyde struggling after freedom; and at last, in an hour of moral weakness, I once again compounded and swallowed the transforming draught… My devil had been long caged, he came out roaring. (10.17)
Repressing Mr. Hyde merely makes him stronger and angrier when he is finally released.