That's fine, let them charge
I have been ignoring calls from unknown numbers for years, and relying on people who try to reach me to leave a message, and it has worked fine.
If they charge, a lot of people will pay - if enough do then robocallers will be forced to give up or at least there will be fewer of them. So I'll still benefit even without paying!
There's no way a republican majority commission would give telcos an "unfunded mandate", so there was never a chance of this being free. But something that's not free but has at least a shot of working is better than arguing over whether it should be free or not and doing nothing.