I agree that the private sector has a role to play but I think you're doing whatever the opposite of throwing the baby out with the bath water is (leaving it in the shitty water?). It's undoubtedly a good thing when, say, an old warehouse is converted into housing, and in the absence of the public sector having the will or ability to do it, private investment has been key, and doubtless will be key going forward. If that was the limit of what the private sector did in the housing sphere I wouldn't have too many complaints, I think that such developments should include high requirements for affordable housing, but ultimately I understand that the goal of private investment is to make money and something is better than nothing.
The problem is that such projects aren't representative of the sector as a whole, and certainly aren't representative of the impact of the private rental sector on the average person's life. The sort of private landlordism most people come into contact with is bad for (almost) everyone but the landlord, it pushes up house prices, both by taking properties off the market and because landlords will pay more than homeowners for the same property. The reason I say it doesn't play by the rules is because normally, the price of commodities responds to a variety of different factors (including affordability to a wide range of customers). Landlordism doesn't because rather than having to respond to what is affordable to people in general, it only has to respond to what is affordable for the richest person (or small group of people) willing to live there. Rents are arbitrarily set at a 'market rate' which has no relation to how much it costs to administer the 'service', which shouldn't be par for the course for literally the most basic requirement for human life (and which also has an estimated cost of £9b a year to the taxpayer in housing benefit going straight to landlords). Landlordism is one of the primary drivers behind the community breakdown we see in many parts of the country as people are forced out due to high rents, or because they need to leave their parents' house and can't afford to buy locally. Obviously London is the big example, but my hometown (Durham) is seeing the same thing - private landlordism with student-only policies has made it impossible for the average local to buy or rent a house in the city. As a consequence, the city is dead for 5 months of the year which has killed off a lot of small businesses, the lack of locals living in the city means that most of the businesses and facilities now exist primarily to service students, which in a poor area means a lot of locals are priced out of their own city. The areas where prices have become inflated due to landlordism are also the places in the catchment areas of the best schools, so educational inequality is exacerbated - the school I went to 10 years ago is unrecognisable now. Sorry to harp on a bit, but I'm trying to demonstrate the breadth of the impact of allowing private landlords a stranglehold over your housing supply has had one one small town.
Obviously on top of that, you have all the bullshit that most people who have rented will have experienced with landlords - bad service, poor conditions, breach of contract, illegal charges - which many renters can't challenge because they don't have the money to go elsewhere, but all of the things in the previous paragraph are consequences of landlordism irrespective of whether they are 'good' landlords or not.
Again, I'm only partially railing against landlords themselves here, the point is that it's a bad system with a lot of negative impacts on both individuals and society as a whole, and allowing it to be such a big part of our housing sector is daft.
In terms of your last paragraph, I'd also be critical of how other basic essentials are supplied in this country, but there aren't many people literally being forced to uproot their entire lives because their electricity bill would be cheaper somewhere else, whereas that happens with housing all the time.