What is the effect of not having to be sworn as a witness at trial?

Wherefore, in Ruloff v. People, 45 N.Y. 213, 221-222, the court said: "By statute (ch. 678 of the Laws of 1869) persons upon trial for crime may, at their own request, but not otherwise, be deemed competent witnesses. The act may be regarded as of doubtful propriety, and many regard it as unwise, and as subjecting a person on trial to a severe if not cruel test. If sworn, his testimony will be treated as of but little value, will be subjected to those tests which detract from the weight of evidence given under peculiar inducements to pervert the truth when the truth would be unfavorable, and he will, under the law as now understood and interpreted, be subjected to the cross-examination of the prosecuting officer, and made to testify to any and all matters relevant to the issue, or his own credibility and character, and under pretence of impeaching him as a witness, all the incidents of his life brought to bear with great force against him. He will be examined under the embarrassments incident to his position, depriving him of his self-possession and necessarily greatly interfering with his capacity to do himself and the truth justice, if he is really desirous to speak the truth. These embarrassments will more seriously affect the innocent than the guilty and hardened in crime. Discreet counsel will hesitate before advising a client charged with high crimes to be a witness for himself, under all the disadvantages surrounding him. If, with this statute in force, the fact that he is not sworn can be used against him, and suspicion be made to assume the form and have the force of evidence, and circumstances, however slightly tending to prove guilt, be made conclusive evidence of the fact, then the individual is morally coerced, although not actually compelled to be a witness against himself."