Rhe scientific community (partly) , the media and the politicians very often argue that the space station's reason for existence is it's capability of doing lots of science.
However, those who've made a little more investigating will argue it's not true. Scientific experiments haven't produced good results over time and it's true unmanned missions have done much much better.

Maybe science is only what is sold to the public but the real reason for a space station is elsewhere.

A Russian has said (forgot who and when): "I confess I don't know why we built a space station but I'm convinced we'll make great discoveries around it and then the reason will become obvious".

One day, the space station's biggest merit will shine above any other: that it exists, that it is a destination, a place to go.

Maybe that's why it's built, so that it exists.
I do regret the ISS wasn't built by attaching modules to MIR and expanding from there, discarding old modules, replacing them. 0G and vacuum allow for a lot of creativity.

It reminds me of how Arthur C Clarke often ends his stories:
"He didn't know what he'd do with his newly acquired power, but he will think of something".

Raoul