I don't think anyone doubts this mate, it's just Labour's usual fairytale economics which make the idea so idiotic. There's two questions here,
(a) should the provision of a national infrastructure such as communications, be owned and run by the government? Based on our experience of pretty much every single thing the government has run ever, then the answer to that is a pretty obvious "of course not", despite the loons believing otherwise.
But let's park that for a moment. The other question is
(b) Should the provision of this communication network be free? That is a completely separate question from (a).
The answer to that question is also "of course not". Very many people do not need such a subsidy, and that would mean throwing money away which could very well be spent on something else like healthcare. Moreover, the idea of Labour buying assets but that the cost doesn't matter because these assets will be generating a return (a dubious justification, but never mind) goes out of the window if there is no return. As an enormous cost-guzzling organisation with no revenue, a nationalised BT would necessarily be competing for funding with the NHS, the police, armed service etc. It costs £20bn PER YEAR to run BT, by the way. Inevitably it will end up with less and less investment and will fall behind. This is so apparent from everything the government ever owns, it always turns to shit. Wouldn't it be great if we could learn from those lessons for a change?