Invading Germany when they remilitarized the Rhineland wouldn't have made much sense. The Germans and British were basically peas in a pod in WWI.
Wannabe dictators were coming to power all the time, but very few of them launched world-conquest attempts. Not even Stalin did that. So, while we have hindsight that stopping Hitler in particular could have avoided WWII, nobody alive at the time would have any reason to think that stopping Hitler was more important than stopping any particular other dictator.
What if we'd engaged in a campaign of detalibanization and enforced liberalism outside of Kabul?
"be liberal or die" that sort of thing? What an oxymoron.
"Forced liberalism" in Afghanistan would entail bringing in enough westerners to enact a complete martial-law government, with massive amounts of security personnel, and a surveillance state. The end result isn't "forced liberalism" at all despite whatever intentions were in place, the end result would be a technocratic surveillance police state with capitalism.
the Westerners you'd need to bring in to run something like that are in fact the reason this "forced liberalism" thing doesn't work. The job description of having complete power over a captive population in fact attracts rapists and murderers to run the place, and you get secret prisons, torture and the like, with a "liberal" facade.