Well, I would in the terms that taxes are literally that. Our taxes pay for the service, you shouldn't need to pay again to use it. You already paid for it. I wouldn't replace taxes with a proportional fee structure either. This is what living in a society is. Sometimes you'll put money towards something that you'll never use, sometimes you'll use something far more than what you paid for. A government and really, a society, or community is only as inversely strong (weak?) as its most selfish person. I've seen a lot of people recently who are applying logic that they wouldn't give 100 starving people a meal if one of them didn't "deserve" it. We need to fix this mentality or we are doomed as a society and frankly, with that line of thinking, I'd question why government bodies even exist since the people pay most of the taxes.

income-proportional fee structure for government services?

This is income tax.

Caltrain and Metrolink (California, USA regional trains) have the right idea. Low income Americans by and large carry EBT cards. They give a 50% discount on tickets when scanned. Of course this could be technologically easily made free but it's a start and the remaining challeges are financial and political.