Since the final two chapters of The Strange Case of Dr. Jekyll and Mr. Hyde, Chapters 9 and 10, are written, first, from Dr. Lanyon's voice and then from Dr. Jekyll's voice--both by means of an epistolary (letter) literary technique--Mr. Utterson's point of view on Jekyll's experiments can only be inferred from what the narrator says about him and from what he does and says in previous chapters. We can only infer because the narrator never comes back to the narrative to say how Mr. Utterson reacts or what he thinks or feels about the experiments he has just read about.
One of the first things the narrator says about him in Chapter 1 is that Mr. Utterson is tolerant of his friend's misdeeds and more likely to help them out rather than to reprove them. Since he has these character traits, the narrator says that he is often the last friend of men whose lives take a downward turn into misfortune:
"[Utterson] used to say quaintly: "I let my brother go to the devil in his own way." In this character, it was frequently his fortune to be the last reputable acquaintance and the last good influence in the lives of downgoing men. And to such as these, so long as they came about his chambers, he never marked a shade of change in his demeanour."
In Chapter 8, when Utterson and Poole are going through Dr. Jekyll's experiment cabinet, on the other side of the courtyard from his home, looking for clues to Dr. Jekyll's whereabouts, one of the last things Utterson says is, "O, we must be careful. I foresee that we may yet involve your master in some dire catastrophe." The reader may infer from this that Utterson has remained true to the narrator's first description of him in Chapter 1: He is neither judgmental nor alienated from Jekyll, even with the possibility of Jekyll's having committed the murder of Mr. Hyde hanging in the air.
From these things, and other similar instances throughout the text, it can be inferred that once Utterson has read Dr. Lanyon's letter and Dr. Jekyll's confession he will remain true to his character and true to his name and continue to be utterly devoted and forgiving in his friendship to Dr. Jekyll in spite of the horrors of Jekyll's experiments.