Quotes

"A principal source of errors and injustice are false ideas of utility. For example: that legislator has false ideas of utility who considers particular more than general conveniencies, who had rather command the sentiments of mankind than excite them, who dares say to reason, 'Be thou a slave;' who would sacrifice a thousand real advantages to the fear of an imaginary or trifling inconvenience; who would deprive men of the use of fire for fear of their being burnt, and of water for fear of their being drowned; and who knows of no means of preventing evil but by destroying it.

The laws of this nature are those which forbid to wear arms, disarming those only who are not disposed to commit the crime which the laws mean to prevent. Can it be supposed, that those who have the courage to violate the most sacred laws of humanity, and the most important of the code, will respect the less considerable and arbitrary injunctions, the violation of which is so easy, and of so little comparative importance? Does not the execution of this law deprive the subject of that personal liberty, so dear to mankind and to the wise legislator? and does it not subject the innocent to all the disagreeable circumstances that should only fall on the guilty? It certainly makes the situation of the assaulted worse, and of the assailants better, and rather encourages than prevents murder, as it requires less courage to attack unarmed than armed persons." - Cesare Beccaria - Essay on Crimes and Punishments

I got to this by looking for the source for this quote...

"Laws that forbid the carrying of arms...disarm only those who are neither inclined nor determined to commit crimes. Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than prevent homicides, for an unarmed man may be attacked with greater confidence than an armed one."

...which is attributed to Thomas Jefferson. What led to this short search was the quote's appearance here. So, it's not a quote by Jefferson but that doesn't make it any less true.