Why people keep saying that Unions are no longer needed when I make DOUBLE a non union person in my city?

Those who are anti-union will accuse you of making too much money on the backs of the tax-payers. But I would much rather work in the public school system. There are some private school teachers that make as little as $20,000 a year. That is not a liveable wage and definitely not appropriate for someone who has gone through so much education and hard work.