This shouldnt be a poll. I understand what you are trying to ask but your question is fundamentally illogical. Lets think it through.
Premise 1: Ich is inherently present. Obviously Ich isnt always going to be in a tank. If I have an empty tank full of RO/DI water and salt there will be no Ich. So it has to be introduced. In addition, Ich is a parasite and needs a host to survive. A tank without an adequate host can not sustain Ich (separate frag tank system).
Premise 2: The introduction of Ich can not be avoided. This premise is also flawed. Ich is not airborne so must come in via an introduction to the tank. If I add dry rock that has been bleached it obviously will be devoid of life. Someone who maintains a fish-less system will not have Ich.
So we have established that there can be an Ich free system (your poll question). The interesting question is whether or not it is feasible to try to maintain an Ich free system. Meaning can you QT sufficiently to prevent entry or are you willing to maintain a fish-less tank.
To QT to prevent Ich is the question at hand. There is plenty of literature available because of commercial fisheries. The Ich life cycle estimates vary from one study to another but is agreed to be roughly 6-8 weeks. Anything would have to be QTed for a mininmum of that time to eliminate Ich. But people do not realize that Ich life cycle functions on a bell curve, as does most of biology. Think of height in humans. The average height may be 5'10'', but there could be a family that are all above 6'6''. The same works with Ich. It is possible that one "strain" could have a life cycle of 10 weeks. So it is impossible to ever guarantee all Ich will be eliminated via QT. The best you can do is lengthen the QT to increase the probability that all parasites are dead. This applies to anything wet going in the tank.
This does not work for fish, who act as hosts. A fish with a healthy immune system may act as a psudo carrier for Ich. If one parasite is survives it will not produce visible symptoms. This parasite will take several weeks to pass through a life cycle and produce the parasite form (Trophont) that is visible on the fish. This would mean the fish would appear healthy for more than 8 weeks even though Ich was present. Theoretically a fish could go on for years with a baseline small infection. The other option is to treat all fish, but treatment carries some risk of not completely eradicating Ich. Copper or Hypo carry more risk of leaving some Ich alive because they allow for variability in parasite susceptibility and correct dosage levels and times. Tank transfer, as far as I can see, would come closer to a guarantee of no Ich if done for a long enough interval and under the right conditions.
Thus, the question for your poll should be "Experiences on the effectiveness of an 8 wk QT" or "Opinion: Is QT for Ich really worth it" rather than "Is Ich always present in a marine tank". HTH