Doing so will result in a greater good to society. Those who have been given the privilege that others don't have ought to contribute towards others having the same or some opportunity. And paying taxes to a neutral body like the government can and has been an efficient way to spreading utility. I think society should value both individual effort and collectivism.
"Give a man a fish, you feed him for a day. Teach a man to fish, you feed him for a lifetime."- Confucius. Giving money will not help reduce poverty. It is just a short-term solution. Teaching the poor about different jobs is a better solution. Once the money is spent, more money will be required. This doesnt mean the money earned by a person should be used to help another.
But if everyone was required to give at least 10% of their salary for poverty, then they might not do it while feeling satisfied. People will give 10% because they are required to. And that is also because 10% is not a small amount. In addition, it depends on the salary of the person. Not everyone has a good salary. I agree with the previous argument, that to help the poor is by teaching them how to make money out of their resources.
This is literally Communism (correct me if I'm wrong). From each according to their ability, to each according to their need. I should keep the money that I work for and give as I please. The government has no moral right to force me to give that much of my income to someone less fortunate