Oppression of the majority supported by moral threats.
Not sure how you'd define poor, but if you would find a median wage in a country and divide the population into 'below' and 'above' the median wage, then you'd probably end up with a 30%-70% or 20%-80% distribution depending on how free the market is (probably 15%-85% in the USA, 40%-60% in Scandinavia).
Which means that the larger voting base, those in the majority will always be those less-off when it comes to wealth. And the majority will always seek to impose their will on the minority. While this is opposed by modern society, the oppression of the rich is usually ignored because they 'have enough to share' and because 'wealth redistribution is morally superior'.
For the latter one, I usually give two answers, a parallel and a logical argumentation that wealth redistribution (and even percentage-based taxation) is immoral.
There is an apple farm where a hundred apples are produced each day for ten people to consume. Before you accuse me of anything, I'm basing the figures off USA statistics (with apples gathered standing for tax paid).
The ideal is for a person to consume 10 apples a day, and each person to produce 10 apples as well.
However, in this orchard, One person gathers 71 apples each day, while four people gather no apples at all. The remaining five gather an average of 5.8 apples.
Is it a righteous goal to create income equality and re-distribute the apples so that each person gets 10? Is it morally superior to tell the person who gathers 71 apples a day that they should not eat 21 but 17 and give 4 more to the community?
And there comes the logical deduction.
1. Theft is immoral.
2. Theft is taking a commodity without proper compensation
3. The government takes the commodity of money as tax, and distributes government services as compensation
4. If all citizens get the same government services, then these services have a hypothesised value of X.
5. Any citizen paying in taxes above the hypothesised value of X is being robbed, any citizen paying below comes better off.
6. Percentage based taxation creates a different tax-input for each citizen
7. Because of this, only a very small group of citizens will input exactly X.
8. And therefore, percentage based taxation will always leave people being robbed.
9. And because theft is immoral, this system is immoral.