Bill Finger just wanted to give Batman an aid to talk to, he wasn't trying to lighten up Batman. Robin's presence changed the tone by adding more humor as this kid beat up grown men, however, the Batman stories from 1940 and 1941 still had a dark atmosphere, taking place at night and included killings, murder, suicide, etc. Bill Finger saw Batman as more than merely a Sherlock Holmes type. Bill Finger also saw Batman as a mysterious and eerie creature of the night like the Shadow. The Shadow specifically was a major influence on Batman. Denny O'Neil explained, “Make no mistake, Batman is The Shadow’s direct heir. For that, we have the testimony of an ultimate authority, the writer who first put words in Batman’s mouth. His name was Bill Finger and he told historian Jim Steranko, “I was very much influenced by the Shadow…I patterned my style of writing Batman after the Shadow…My first script was a take-off on a Shadow.””
http://www.prlog.org/10110966-the-sh...of-batman.html
The first Batman story, "The Case of the Crime Syndicate" (1939) is a blatant lift of The Shadow pulp story "Partners of Peril" (1936). As Anthony Tollin discovered, "It turned out to be the same story with basically nothing changed. I mean, it was a chemical syndicate in both stories! Finger didn't even change it to some other kind of business. And The Shadow is described as 'bat-like' in the rooftop scene where Batman makes his first appearance in costume.
Well, it clearly establishes that without The Shadow, there would be no Batman! Since the first Batman story was a start-to-finish lift of an earlier Shadow novel, it establishes that the similarities between the two characters were no accident. Bruce Wayne is wealthy young man about town Lamont Cranston. The friendship between Bruce and Commissioner James Gordon (whose name comes from The Shadow's sister magazine, The Whsiperer) is no different from the relationship between Cranston and Weston. Batman's talent for escapes also comes from The Shadow, since the first recorded Batman escape duplicates The Shadow's in the same story. And the Shadow lifts continued in subsequent stories, even ones written by Gardner Fox, which gave Batman an autogiro, Bat-a-rangs like The Shadow's cable-outfitted 'yellow boomerang,' and a suction-cup device for scaling walls ... all Shadow gimmicks. Without the Knight of Darkness, there would be no Dark Knight."
http://www.comicmix.com/news/2007/06...cal-syndicate/
Batman was still the mysterious creature of the night lurking in the shadows after Robin's introduction, and Batman was a vigilante fighting the police in the 1940 to 1941 comics, and there was a lot of killing, even Robin killed.
Batman #7 (October-November, 1941) "The Trouble Trap" by Bill Finger, Bob Kane, Jerry Robinson and George Roussos:
Detective Comics #50 (April, 1941) "The Case of the Three Devils" by Bill Finger, Bob Kane, Jerry Robinson and George Roussos:
Batman #4 (Winter, 1941) "Victory for the Dynamic Duo" by Bill Finger, Bob Kane, Jerry Robinson and George Roussos:
Graham Masters shoots himself in the head during a struggle with Robin in Batman #6 (August-September, 1941) "The Secret of the Iron Jungle!" by Bill Finger, Bob Kane, Jerry Robinson and George Roussos:
Mr. Wylie commits suicide rather than face trial and imprisonment. "Much better this way!" murmurs Batman to Robin grimly in Detective Comics #42 (August, 1940) "The Case of the Prophetic Pictures" by Bill Finger, Bob Kane and Jerry Robinson:
In another adventure with Robin, Batman kills many of the Green Dragon tong's members by overturning a gigantic statue, which crushes and kills them in Detective Comics #39 (May, 1940) "The Horde of the Green Dragon!"
In Batman #2 (Summer, 1940) "The Wolf," by Bill Finger, Bob Kane and Jerry Robinson, Batman unleashes a punch that sends Adam Lamb plummeting down a flight of stairs, breaking his neck and killing him. Robin says "I feel sort of sorry for him!" "This is the only time I was ever sorry to see a criminal die!" murmurs Batman grimly. "Medical attention might have cured him!"