Space is huge, but space is also empty. Mining asteroids is really energetically expensive if you want to get the material back to Earth. It’s a very reasonable thing to do if you want to build stuff in space, though.

> a lot more resources open up. Mining asteroids is just one idea there

We should certainly explore and hope to discover rich deposits of varied resources that are worth expending the time and energy to find, extract, and use. However, to our knowledge, asteroids probably consist of clay and silicate rocks, some containing nickel-iron[1]

[1] https://science.nasa.gov/solar-system/asteroids/facts/

But not infinite resources. ..

If we accept the hypotheses of an expanding universe then we find ourselves in a pickle as our potentially infinite resources race out of our light cone faster than we can chase them.