Personally I'm for it, but also against it, weird huh? Let me explain. I'm for it IF, and that's a huge if which I'll explain later, if the fee is a one time fee at the time of purchased base on the purchase price of the the bike, and then only for adult bikes. A 5% one time point of purchase fee that would register the bike's serial number for aid in helping to find a stolen bike and get it back to it's rightful owner would be a big plus. But mostly the money gets used to help improve, not totally fund but to assist current funding of bike trails, paths and lanes.
Problem is who will run the fund, the government, that's a huge problem and it's why I'm against it. The government will find ways to steal the money claiming they need it for more important projects. The federal government already gives states highway money, part of that money is to be used for bike infrastructure improvements, Indiana this last summer stole that money and diverted it to road projects saying the road projects were more important. And that's not the first time that a state, or the feds, stole tax money, and it won't be the last. Also the feds could come back and say, well gee you don't need any fed money for the bicycle stuff because you got plenty of money from the fees...there goes any chance of improving the system.
I am also against raising taxes like sales or property or whatever to fund bicycle infrastructure because currently in America only 1% of the population commutes by bike, the demand isn't anywhere high enough to justify raising taxes to pay for something rarely used.