Well, probably, yes. But only because the keeper hasn't gone to the effort to remove it. It can be removed, although typically it costs the person all their fish first, as it did for me. With proper quarantine, you can have a parasite free tank.
The question might be, can my fish be fine even if I have ich in the tank? Again, probably. I've had ich outbreaks that I've cleared up with garlic, no fish losses, and no sign again of ich for years. So yes, your tank can be ok with ich present, assuming the fish are healthy and stress free? Does that mean you shouldn't do more? No, not really.
As it was stated, it is our responsibility to do our best. Most of don't, for many reasons. Time, space, money, laziness, lack of concern, etc..
All depends on what you want, what risk you're willing to live with, and whether you want to chance killing all your fish, and then replacing them. That last part cost me about $2000
I'm not willing to do that again, so I go through the trouble, or if I don't want to go through it, I don't buy more fish.