"...is it really fair to pass a tax that will disproportionately affect people in a small number of professions? (teachers, policemen, firemen, etc.)"

YES, it is fair and it is called redistribution. Similarly, it is fair to tax the wealthiest individuals "disproportionately". People in these professions have enjoyed inflated benefits, relative to the rest of us, for a long time. The problem is that now they feel entitled to such benefits, even though most of the population does not have them. You cannot hope to get sympathy with your argument. I hope you realize that.