The US did shut down its WWI-era spying in 1929. The (Republican!) Secretary State did so with the simple comment "Gentlemen do not read each other's mail".
> Enemy nations can then go rampant
The main enemy of the FVEY agencies has always been the population of the FVEY countries. This goes back a long time - in the era that US Republicans actually did believe in smaller government and Stimson was shutting down the Black Chamber, British intelligence was manufacturing the Zinoviev letter to bring down the Labour government in 1924. Peter Wright discussed more modern efforts by MI5 against the Labour party in Spycatcher, especially in the 1970s, and this has been discussed in other sources.
Similar machinations were happening in the USA in the 1970s, with Nixon using ex-CIA operatives to, among other things, break in to the national Democratic campaign headquarters in order to rig the election his way. That's against the background of COINTELPRO, spying on blacks seeking their civil right to vote and such, or that part of the electorate that wanted to withdraw from a war in Vietnam that the top brass and chiefs were privately saying was a lost cause. FVEY intelligence also helped bring down Gough Whitlam's Australian Labour government in the 1970's, an American, Christopher Boyce went to jail for, among other things, revealing this news to the Russians.
Insofar as enemy nations, England has had a litany of enemy nations in the 20th century - Indians who wanted independence, Argentinians who wanted the Malvinas returned, Irish who wanted English troops out of Ireland and on and on - think of John Cleese in the Meaning of Life waning on about efforts to "keep China British!"
US intelligence caused Daoud Khan to turn his back on the Soviets who had helped propel him to power, and when the Russians backed another horse and their former friend was ousted, the US said the "enemy nation" of Saur Afghanistan with Soviet backing was "going rampant", so the US helped launched a mujahideen-led jihad against secularizing Afghanistan, financing and arming Osama bin Laden and other proto-Al Qaeda and Taliban forces. Then years later the US decided to plant military bases in Saudi Arabia, causing this Arab nationalist to send his fighters with planes into the Pentagon.
Now we're told we need we need to work and be taxed to finance these FVEY agencies to protect us from these dangers which they themselves created. Whereas the real enemy they are fighting against is their own populations - as MacDonald, McGovern and Whitlam could all attest to.