Me paying the same multiplier of my income as you is NOT by any common definition of the word “fair.” One of us is still paying a different amount of money than the other person.
I challenge you to find any scenario where you would apply the same math and call it “fair.”
I can design 50 different tax systems and apply a constant multiplier to create the illusion of “fairness,” and each tax system would look radically different. They can’t all be “fair” if they look absolutely nothing like each other.
The only “fair” system is for every person to pay exactly the same amount.
Once you accept that, then you have to answer the next question; why don’t we have a fair system in which everyone pays the same amount? When you have the answer to that, whatever that answer is, you have to accept that you, in fact, don’t support a “fair” tax system, but rather you support a system where people who have/make more money pay more into the system.
After you have reached that conclusion, you then decide, again for what ever reason, how much more people with more money should pay. Arbitraily applying the same multiplier to everyone in order to genrate more money out of rich people, though it may convince you otherwise, is simply not a fair system. It is no more fair than applying the same graduated system to everyone equally.