There seems to be a common misconception that Libertarians don’t like government or believe they should be involved in our lives at all. It is true that they believe government involvement should be minimal but certainly it should be there.
To start with there’s a misconception that Libertarian ideas regarding taxes makes it impossible for the government to provide for the common defense. (Such as a military.) Libertarians oppose the income tax and perhaps a few others that I’m not aware of. There are many other taxes they do not oppose.
I'm not really sure what their stance on the environment is. However I don't think it would violate Libertarian ideology to recognize that pollution can be a rights violation and as such take actions to prevent or curtail it. This doesn't have to entail a monster organization like the EPA to be effective.
With regard to businesses setting up monopolies. Most of the so called Robber Barons did so with the help of various politicans they bribed. If the power of politicans to interfere in business was limited so to would the incentive to bribe them. You wouldn't get rid of all corruption but you'd certainly get rid of some.
Marc