Fitzy54 NICs are capped. Very rich people don't pay any more than moderately rich people. In any case they find other ways of being paid, such as in dividends or by deferred pension contributions.
If you think people should keep the money they earn, how do you propose paying for schools, the NHS, roads, the police, the army, social care, border control, pensions, administration of elections (this is costing a lot at the moment), etc etc.
As manual tasks become increasingly robotised and there is less need for unskilled people, should we just let unskilled and disabled people die? After all, it doesn't make sense to keep them in a fully "dog eat dog" market economy.There's not a lot of point keeping the very elderly and ill alive either. 
The government isn't in the business of making a profit, but redistributing wealth and opportunity for mutual benefit, based on the values a society chooses to adopt. Maybe you'd prefer to live in a third world country, where tax is rarely collected.