A major issue that many have with tax at "perceived" high income is that it then stacks on top of other taxes that also ratchet up quickly, and of course there is no mechanism in income tax to adjust for cost of living variances across the country which makes it far from equitable.
Someone earning 80k in Burnley, where you can buy a three bed house in cash (with no SDLT if FTB) with your year's take home, pays the same amount of income tax as someone who lives in zone 1 or 2 London on the same salary, who needs 20x that plus a huge SDLT bill. 80k in Burnley is objectively a high income, 80k in Zone 1 or 2 is definitely not.
Considering SDLT more, as one of these stacking taxes, with a more real-world breakdown. First time buyer in say Plymouth could can comfortably get a 4 bedroom detached with a double garage for 375k and pay £3,750 in SDLT. In Zone 2, a "normal" 2 bedroom apartment that sells for £750,000 would attract £27,500 in SDLT for a first time buyer. Nearly 7.5x as much tax for something only twice the price. So even if that person earns double (let's say 50k and 100k), under the Corbyn proposed tax regime, in the year that the property is purchased the person on 100k would have paid 28.5k in income tax and 27.5k in SDLT, and the person on 50k would've paid 7.5k in income tax and 3.5k in sdlt. 56k vs 11k. More than 5x the amount of tax for earning double, and getting a much smaller property. Is that REALLY equitable?
People will just say "well don't live in London then". In which case they earn less for the same thing. Which means they then pay WAY less tax, which doesn't work for the socialist agenda....