Feed-in tariffs are a subsidy - they pay out more than the actual market value of the electricity, and that money comes from the bills paid by other consumers. This is especially true of the ones on older UK solar installations, which are higher than the retail cost of the electricity. There might be some justification for arguing that the ones in other places with much greater reliance on air conditioning and a summertime peak in usage aren't, because they could act as a form of peak shaving, but that doesn't apply to the UK.

This didn't happen because the numbers added up. The government mandated it for political reasons and all parties had to go along.

The sad thing is, the feed-in tariff subsidy would be less than UK's existing fossil fuel subsidies for homeowners. Yet solar is worth doing today in the UK, even with no subsidy if you project to stay in the house long enough to pay back capital cost.

With current solar pricing, it would be better for everyone if they simply moved a requirement for solar into the building regs. Like they've steadily done with insulation levels- though these are not yet adequate.

A large chunk of the UK's existing "fossil fuel subsidies" for homeowners consist of the government charging a lower 5% VAT rate on domestic electricity and heating, much of which of course comes from fossil fuels. Take that away and spend the money on feed-in-tariffs, and you're again transferrirng money from the less well off to the wealthy.