Monopolies promote waste and abuse. Taxation is extortion. A tax-funded monopoly is inherently evil, regardless of the service it provides.

Corporations supported by government subsidies, bailouts, protectionist regulations, etc. distort the market by denying consumer choice and externalizing their costs. The added burdens on business through regulation, taxation, trade restrictions, etc. harm those at the margins - the small businesses and startups - that would otherwise be able to make headway in the market. This guarantees overpriced, shoddy goods and services too. Corporations are aspects of the State, not market phenomena.