The phrase to cut both ways means:
– of a point or statement: to serve both sides of an argument,
– of an action or process: to have both good and bad effects.
It refers to a sword which has two cutting edges, as is clear from its first known use, in Priest-Craft, its Character and Consequences. The Second Part (London, circa 1706), by Edmund Hickeringill (died 1708), Church of England clergyman and religious controversialist; A Satyr against Fame thus begins:
Fame, like a two-edg’d Sword, does cut both ways,
And equally, doth praise Men, and dispraise,
Cæsar and Pompey were surnamed Great,
By Sycophants, and in their own Gazett,
Being great Butchers, they great Fame did get.
The following is from the Kentish Gazette of Friday 31st March 1797:
To the Printers,
Sirs, London, Thursday Evening.
To prevent all misrepresentation of what passed at the Common-Hall this day, I send you the opinions of the several Companies as they marched before me.
I am, your’s [sic],
The Beadle at the Great Stand.
The ‘Merchant-Taylors’ conceived that this Hall could not ‘suit’ the purpose of those who requested it; and that it was not right to be always sticking in the ‘skirts’ of Ministers.
The ‘Coopers’ thought that every ‘tub’ should stand on its own bottom.
The ‘Shipwrights’ thought that although there might be a ‘leak’ in the vessel, the present crew were fully competent to ‘stop’ it.
The ‘Cooks’ never heard such a ‘mess’ of complaints, and thought the greater part of them ill ‘digested’.
The ‘Cutlers’ looked ‘sharp’ after such gentlemen whose arguments seemed to ‘cut’ both ways; and gave their votes in a very ‘blunt’ way.