Are lockdowns justified?

[FlatAssembler]

If Europeans go nuts over them and refuse to abide, again, that's not a failure of the lockdown.

Sure, if humans weren't humans, lockdowns may very well work. But humans are humans, and so lockdowns have little or no effect. And, when discussing politics, we must not forget that humans are humans.

There were fewer cases during summer because lockdowns in the prior months reduced spread

I don't think this explanation is correct, as the same is true for countries which had no lockdown, such as Sweden:

people don't gather inside as much in the summer

And you don't think lockdowns result in people gathering inside secretly? If so, they are counter-productive because humans are humans.

We shouldn't try to describe a complex situation with a few simplifications

But that's how science works. Science builds simplified models of reality which can actually be used to make predictions. A model that is too complicated to make any prediction is not science.