In actuality, we need BOTH things. There's actually enough resources for maintaining low gravity manufacturing, etc. on the Moon (which we actually need to start getting to if you're going to travel to the stars in the first place...) and we need those experiments on the ISS (Which isn't zero gravity (If it was, you wouldn't need to constantly push it back into orbit...), but close enough to count for what we're needing right now...) for the reasons you give.
The brutal truth of the matter is that we're pouring money into "social" programs that are hopelessly mis-managed and we keep trimming the budgets for doing this stuff because "it's unnecessary" (Never mind that we're where we are mainly because of the space and defense budgets of the world...). Something we need to realise isn't a useful utilisation of our collective resources as a species.
We spend $1100+ Billion on some of those social programs ($500 Billion on Medicare, $620 Billion on Social Security, and let's not count all the others).
We spend $19 Billion on NASA (which, incidentally, works out to the amount we spend every 14 months on SS vs the duration of NASA). It's like cutting one vending-machine Coke from your budget when you have have payments on a pair of brand-new cars.