I'm saying I want to discuss and debate science on the basis of an eternal universe with boundless space
And in order to assume that basis in arguments, you have to defend that basis in an argument, and win.
That's how it works. If you attempt to defend a steady-state, eternal universe in arguments and fail, you don't get to simply assume it as a basis for other arguments. Sorry, but that's the price of losing. You're free at any time, I suppose, to discuss
what it might be like in a hypothetical steady-state universe; but you need to make it clear that you're not talking about the universe we inhabit, because then the discussion becomes evidentiary and not hypothetical.
Honestly if you wanted to speculate about what it might be like in a steady-state universe, I'm sure you could find a bunch of people to do that here. It would probably be interesting. But if you want to proceed from a basis that
the universe we live in now is steady-state, then you need to win that argument first. You don't get to simply presume it as a basis for other arguments until you win.