> The objective truth in the 70s was, "smoking is good for you". Since then, the narrative changed.

Your misunderstanding of the history doesn’t mean it was ever good for you. People didn’t call cigarettes “coffin nails” because they thought it was good for you and e.g. the specific lung cancer link was known at least as far back as the 1920s. The reason why it wasn’t named earlier is the same reason you’re wrong about it today: it was an enormously profitable industry and they were able to produce the ads you’re remembering which got far more attention than those pesky scientists who had been correct for half a century by that time – and many smokers blamed people for not telling them earlier, even though they had downplayed the warnings given at the time. A very similar story unfolded with climate change where people like to say that it was confused or contradictory for a long time when it was settled by the late 1970s because they didn’t want to admit having given equal weight to the fossil fuel lobbyists as they did climate scientists.

That’s the key distinction here: we have processes for verifying and testing theories. Yes, scientific research has had fraud but we know about those because their work has been critically examined. We should expect that everywhere rather than giving up on the concept.

I would say it differently. Even using your example, "smoking is good for you" is objectively less true than "smoking is bad for you". We know that now.

The problem is that 1) we don't always have enough data to know what is true, and 2) we have a lot of people working as hard as they can to obscure the truth in order to push their own agenda.

All those post-modernist philosophers that I scoffed at were on to something: If we cannot determine the truth from the data available to us, then in practice, there is no truth. That may not have been the point they were trying to make, but for us who are living in it, it works out the same.

> The objective truth in the 70s was, "smoking is good for you".

Bollocks. Even as early as the 1950s there was a widely known link between smoking and cancer, and a 1964 Surgeon General's report said, unequivocally, that smoking causes cancer.

Hell, even in the 1600s tobacco was regarded as potentially dangerous. King James the VI of Scotland and I of England wrote, in 1604, the ‘Counterblaste to Tobacco’, where he talked about its negative impacts.

The "objective truth" was that capitalism doesn't care about your health, and ad campaigns were able to squash every attempt at getting people to quit.