BooNZ
Banned
My guess would be that those choosing it are at least sympathetic to the Ferguson Thesis that Britain need not and should not have fought alongside France and Russia in the First World War. Might even be channelling the Chris Clark Sleepwalkers idea that Britain's commitment to the Entente emboldened France and Russia to support Serbia while Grey's prevarications over whether Britain would join France left Germany willing to take the risk of invading Belgium.
Indeed I voted for the Entente and have both Sleepwalkers and The Pity of war on my bookshelf. I was equally influenced by Dreadnaught (R K Massie), which illustrates decisions are ultimately made by individuals, not a borg-like consciousness. The British decision to align with France and Russia had more to do with the Francophile views of a select few decision makers than any strategic logic.
OTL it was in the collective interest of both Britain and the CP powers to maintain the status quo in Europe. The same could not be said of France or Russia, which openly sought adjustments in A-L and the Balkans/ straights. Avoiding the Entente would mean Britain (and perhaps Europe) either avoid WW1 entirely, or alternatively, Britain is only required to perform light duties for the CP powers. Either way, Britain would emerge from an alternate WW1 stronger than before.
As far as overall negative impact on Britain and empire, no other foreign policy decision comes close - even appeasement.