The problem is not the general idea of paying sales tax. It's the complication of having ten thousand different sales tax jurisdictions. Complying with the law should not be such a nightmare you need to hire a middleman.
- mapping an address to one or more jurisdictions
- digital deliveries might not have a shipping address
- tax rates often depend on the type of product
- product types have different definitions in different jurisdictions
- some taxes are time dependent (back to school tax holidays)
- some buyers are exempt in some jurisdictions for some products