There's definitely a very serious public concern with money going to private landlords.
If you consider WHY so much money is going to them, it is because private landlords expect to make hundreds of thousands of pounds in profit (capital gains), on an investment that is funded for them by the state. That's not a problem in itself, plenty of private companies make big profits from providing services, but when the private sector is actually creating the demand, then questions should be asked.
Example: SomeCompany builds a hospital and charges the government £1 m per year to run it. Fine: we need hospitals, people get sick and die, not problematic.
Different example: Joe Bloggs buys a flat for £150k and charges the government £12,000 per year to rent it out to a social housing tenant. The social tenant hopes in future to buy his own flat, but can't currently do so due to personal circumstances.
Hundreds of thousands of other Joe Bloggses also do BTL, meaning that the market value of the flat rises to £250,000. Now to social housing tenant can NEVER afford to buy his own flat, so the private sector landlords are actually increasing the demand for their own services. This is equivalent to the PFI hospital company giving people cancer so it can create demand for more hospitals.
There were 1.8 million households renting in the private sector in 2001 in England. By 2011 that had almost doubled to 3.4 million, while the number of households living in a mortgaged home had actually SHRUNK, from 8.0 million to 7.2 million.
Basically what happened was every single new home in Britain that was built went to buy-to-let. (Ok, there was turnover, so some buy-to-lets are old homes, and some mortgagees are new home owners, but the increase in households 2001 to 2011 was exactly equal to the increase in number of BTLs.)
There's no doubt that BTL is bad for society. That spiralling housing benefit bill, now £25 billion and counting has spiralled, not because of spongers on Benefit Street, but because of a different kind of sponger - middle-class property speculators. And don't be deluded that they aren't spongers, the fact is that they buy housing at such ludicrous valuations that they are collectively 'too big to fail', and therefore subject to endless government bail-outs in the form of negative real interest rates now for five years and counting, 'Help To Bubble', billions in benefit payments without which their 'portfolios' would be worthless, and so on and on. The only difference is they aren't subject to weekly interviews and TV exposés about their lifestyles.