"flimsy justification" is a correct phrase and is often used in written English.
Example: The politician's speech was filled with flimsy justifications for their controversial policies, leaving many skeptical and unconvinced.
If Mary Magdalene was a woman of hard virtue rather than easy virtue, then the church loses its flimsy justification.
Past performance suggests that the Home Office will plough on regardless, produce a flimsy justification for new powers, and combine it with political threats about the dire consequences should parliament fail to listen.
This ingenious but flimsy justification became the target of an unsuccessful suit filed by the local merchants' organization and argued in the courts by Morris Ernst, who had represented Margaret Sanger in her efforts to legalize birth control and who had won the case that opened the door for James Joyce's "Ulysses" to be published in the United States.
Each has a flimsy justification (they're blocking the road; they stole money from me) and are often atrociously acted.
Instead, it appears to be a flimsy justification a massive system of long-term family incarceration beyond what our nation has ever seen, immigration experts say.
But against a backdrop of a poorly performing economy and tepid economic growth, now is not the time for midnight regulations, let alone unfounded and unnecessary rules that sit upon flimsy justification.
The flimsy justifications for such killings continued, as it emerged this week that Officer Yanez said in his defense that the alleged scent of marijuana made him fear for his life and open fire on Philando just seconds after walking up to his car.
I was waiting for the slightest, flimsiest justification or provocation to buy that bottle of brandy, which was strange, because until recently I'd never tasted much Armagnac.
(Stacked against this is the flimsy legal justification of a poorly worded clause in the 14th Amendment promising repayment of Union Civil War debts).
The Fourteenth Amendment was specifically designed to protect the right to earn an honest living not just for newly freed slaves but for all Americans but today that right receives so little protection that courts will accept the flimsiest of justifications while turning a blind eye to even the most blatant examples of government-imposed economic protectionism.
But it is clear that if and when it is, the flimsy, implicit moral justification of ever more aggressive and inappropriate sanctions - that they affect the "undeserving" poor who are not trying hard enough - would collapse.
