Again, why do you think it's okay to make people pay £150 per year for the BBC when they only watch Sky channels? Would you pay £150 for gas heating each year if your house only ran on electric?
Why would you make people fund schools when they don't have kids?
Why should heathy people pay to fund the NHS? (I am not necessarily saying this is a slippery slope btw, but people in the US literally say this about any kind of socialised healthcare)
Why should London be subsidising the rest of the country on infrastructure projects and things like flood relief?
I am aware that you see a difference between that and the BBC. However, I definitely see broader cultural value in it and I personally think that this is important - so do many on this thread, if not the majority. It contributes to the nation's identity, provides public access to high culture, and is almost certainly a less biased news source than a commercially funded enterprise would be.
If everything were decided based on how much it benefits the majority of people in society, then there would be no programmes to help those who are disadvantaged.
I'm sure people will think this is mad and it's a side thought rather than my core argument, but I also think that if the UK wants to get good trade deals/continue with its 'brand' in upcoming years it would be best to retain its global panache and keep pumping out this type of content. Cultural capital really matters in a global economy. (Amusingly, I just heard a show in Radio 4 which was talking about state support for K Pop and was discussing the economic benefits to Korea of making itself globally culturally relevant. They made no link to the BBC, but it's clear to me!)