“Locks are for honest men/people” is an old proverb in security departments. Burglars (“dishonest people”) can break locks; the locks give the impression of security to keep honest people honest.
 
The “locks” proverb has also applied to laws. A bill outlawing guns, for example, keeps honest, law-abiding citizens from buying guns, but criminals still carry guns illegally. The origin of the “locks are for honest people” proverb is not known, but the proverb has been cited in print since at least 1912.
 
     
Google Books
Word-book of Virginia folk-speech
By Bennett Wood Green
Richmond, VA: Wm. Ellis Jones’ Sons
1912
Pg. 35:
Locks are meant to keep out honest people, not rogues.
     
Google Books
29 September 1951, Billboard, “Tips for Servicing Coin Machine Locks” by Howard P. Schley, pg. 105, col. 2:
Locks, as someone said, were made to keep out honest people.
 
3 August 1954, Springfield (MA) Union, “Chief Cautions Against Looters,” pg. 22, col. 2:
Westfield, Aug. 2—Reporting several car lootings in recent weeks, Police Chief Malcolm Donald today cautioned motorists against carelessness in leaving valuables in parked cars.
 
He quoted the axiom, “Locks are for honest people” in describing the method of entrance into cars. Windows are broken with stones or screwdrivers and glove compartment locks are also forced with screwdrivers.
 
18 April 1961, Baltimore (MD) Sun, “The Eichmann Trial,” pg. 16:
An old Jewish adage sums it up beautifully: Locks are a protection against the misdeeds of honest people.
 
20 February 1962, Aberdeen (SD) American-News, pg. 4, col. 1:
Laws, like locks, are only for honest men. If a crook wants a pistol or a machine gun, he’ll get it through his own illegal means.
   
Google News Archive
16 January 1963, Ocala (FL) Star-Banner, “Tightening Up On Building Security At Schools Ordered,” pg. 12, col. 1:
Asserting, in the old saying, that locks are for honest people, Seay said he and some of his colleagues at the county office picked one of their own locks yesterday afternoon to demonstrate that a break is usually possible if the intruder is determined enough.
 
Google News Archive
16 July 1965, Montreal (Quebec) Gazette, “Pushbutton Locks Keys To Safety” by Jean Shaw, pg. 20, col. 7:
“Locks are for honest people,” says Mr. Lister, and points to the fact that professional burglars take their job seriously.
 
Google Books
Why Your Life Sucks
And What You Can Do About It
By Alan Cohen
New York, NY: Bantam Books
2005
Pg. 63:
Laws and police do not stop people who do not want to be ruled by them; criminals are doing what they want to do anyway (a former car thief told me that “locks are for honest people”).