possible reasons:
1) concern about the neutrality of the BBC, esp. if you don't think they are currently neutral. It also might change the incentives of the BBC if funding is either guaranteed, or controlled by government.
2) the principle of general tax without strong reason. The government isn't trustable, they already privatised much of the railways. consent to general taxation give more power to government.
3) I don't have a television, and more people are choosing not to have one. There are shifts happening both wrt to media is consumed, as well as how laws are changing to adapt (e.g. requiring any device with a screen requiring a licence). Would be better for the situation to stabilise before deciding if a general tax is a good idea.
4) The whole TV-Van issue sours the issue. Public Libraries (AFAIK) don't send people after you for paying fees. The issue of censorship and management of publicly available information are also hot topics in libraries, but there is (arguably) a greater degree of "self serve" in a library, as opposed to planned/programmed broadcast - libraries don't generally create the majority of their content.
