If by American and Western interests, you mean the values western society is built on, the answer should be pretty simple: national security is no excuse for secret courts, secret prosecutions and secret rulings. It's also to be expected that this society is going to provide more opportunities for leaks in the first place, as opposed to more totalitarian societies. Not that there isn't sufficient grounds for arguing that distinction has already blurred for the most relevant purposes.
It's also to be expected that WL's every move is scrutinized. But anti-WL action went much, much further, including a complete financial boycott from above. That was years before any allegations of Russian meddling ever entered the picture. The US has openly targeted them for years, but if they hold any grudge about this in return in the form of not pulling punches and maximizing publication impact, it is supposed to reflect badly on them? That seems more than a little unbalanced.
The skepticism only goes one way. WL has a perfect track record in accuracy. Their own story however is regularly misrepresented and misstated. Plus, never forget that it was a Guardian journalist who was dumb enough to leak the crucial password to the full diplomatic archive, in the same book where they admitted to being too dumb to Google how to open a 7zip file. Such their missteps from the traditional press are casually excused in a game of closing ranks that reminds one more of cops than renegades. So much for the enlightened and free press: they needed a bunch of crypto nerds to show them how it is done, after the tech industry stole their collective lunches, and they handed over control of their platforms and income to hordes of shady surveillance capitalists.
The traditional press' warmongering and American mythologizing is also a naked fact. So much that they even held off on the Trump bashing for a while, when he was banging that drum, calling it "presidential".
So who is really using power over whom? Who is using truth for whuch cause, and who is publishing self serving fluff pieces instead? Why should we worry about WL, when the American fish is clearly rotting from the head down, and those who are supposed to stop that are incapable of doing so?