Here in the UK, there's a whole bunch of sentences that don't involve time in prison. People can be fined or made to work so many hours in community service or prevented from being in certain areas etc.
Those are all examples of something that you would never tolerate being done anyone, unless it were a criminal sentence. Instead of referring to them as fines or compelled service, you would call them theft and involuntary servitude. Being part of a punishment changes everything, and makes the intolerable become tolerable (or even downright desirable and a good idea). If I pointed a gun at your face and said "pick up that trash" or "teach these kids to read" then I think we would later find ourselves in court, where the whole topic of conversation would be my criminal actions rather than the relatively benign actions that I wanted to force you to perform.
Who are you to tell me (hypothetical drunk driver) I'm not allowed to visit pubs? Who are you, to stand in my way and forcefully prevent me (hypothetical pedophile) from enjoying a nice sit on a bench in the playground, where I can admire and chat up the delightfully fresh, juicy children? Oh, you're the government, enforcing my criminal sentence, that's who. Good thing, because if anyone else tried to interfere with my life in such a manner, that person would be in big trouble.
It seems absurd to think of preventing convicted pedophiles from hanging out in playgrounds as "torture" but if a non-government entity followed you around and consistently harassed you (a person not convicted, or even suspected to be, a bad guy) are you sure you might not use "torture" to describe it?
Also, what about government's role in building infrastructure such as roads, airports etc?
If I pointed a gun at your face and demanded 500 quid because I want to hire some guys to build a road, then we'd be back in court again, with you at the witness and me as the accused. Building roads and airports is technically fairly easy (you don't need a government for that) and anyone could theoretically do it ("Tonight on Gardener's World: Monty Don shows you how to build a path around your rose garden."). The hard part is getting the resources (laborer's time, materials, the land itself). We have agreed to allow a special entity go around to force everyone cough up their share of the expense. It's not a crime when that entity does it. It is a crime if anyone else does it. If there weren't so many expenses involved in building infrastructure, we wouldn't have the government do it, because we wouldn't need to. ("Tonight on Love Your Airport: Alan Titchmarsh shows an elderly widow how to construct an eight thousand foot long reinforced-concrete runway.")
It's a dirty job, but we all come out ahead if we get together and agree to make a special entity exempt from the usual prohibitions against doing it.