From the licencing site it says it's 40p a day. Now for some services that may be extortionate, but considering the sheer volume of output from the BBC, its a bargain. And the BBC is used by 96% of people in the UK, so its not something that should be thrown away so lightly. At least with the BBC we have one service which we know we have control over. Who knows if Sky News may turn into Fox News, if murdoch so desires. I know he wouldn't now because there isn't the appetite for such programming here, but at least if general opinion changes, the BBC will still be (relatively) impartial, while I can't say the same for Sky News, or even ITV for that matter.
A subscription will just hurt the BBC, and while people say that as long as the content is good people will pay, they have never heard of pirating. People will just do for sherlock what they do for GoT, go to a torrent site and download it.
Sure 40p a day adds up to a lot overall, but then everything is expensive in the long term. And honestly, for students particularly, if you can't afford it then either you just can't be bothered to budget even slightly, or you honestly need financial assistance, in which case there is help.
As for the entertainment, well I find a lot of BBC3 shows rather boring, yet I know that many would say the same for the shows I like. But at least with the BBC I know they'll produce it all, and so all viewers have something. Honestly the only argument I understand is that due to the flat rate of tv licencing it is regressive, so the only change I would like would be for the licence to be linked to income. You could add it as an extra tax, but then people who don't stream live TV will still be forced to pay.
Also for online only, that is just another thing which hurts most those who proponents for subscriptions seem to be defending. Fast internet is expensive, so you're locking out the poorest from the BBC. Maybe in the future where even the lowest internet speeds allow for good streaming then will online only be ok, but not now.