While the tax rates may be higher, the amount of money they have is much greater. A middle class person paying in the mid 20th percentile, will lose a more important amount of money then the person with more funds at their disposal. Even if we taxed much higher, lets jut say 80% for 1 million+ households, 200k is still 10 times greater then those who earn minimum wage. And 3-4 times the middle class persons earnings. The point is not to punish the rich, but to support those who need it, and to pay for things that are public goods. Not to mention, taxes on the rich would not need to be as high if we were to pay our lowest paid workers much more, and if our middle class also recieved a boost.
Charity made mandatory is no longer charity, and saying 'you belong to this class of people, therefore we will take more from you' sounds kind of classist.
I know a lot of people will think the ends justify the means, but deciding to just take a person's hard earned money because they are from a different class/ group/ whatever, is discriminatory, and the fact that it is against their will makes it theft.
Say person A, who is exactly like person B under the law, takes a risk and it pays off. Person B goes to the big guy, and the big guy says "Give me your profits." The big guy then gives Person B the goods. Wouldn't that discourage Person A from attempting to better his life?