Terri Schiavo simply needs food and nutrition. She is not on "life support." (And she is not unconscious or unresponsive, just not consistently responsive)
To act to pull the tube is unethical because the intention is to cause her death.
The prohibition by Michael for years not to give anything by mouth is questionable as long as the tube feedings continue. In light of the determination to stop feeding, however, it does not look ethical.
It would not be unethical to feed her by mouth, although it risks aspiration pneumonia, because the intention would be comfort and hydration, not to cause a pneumonia.
The
Well, it depends on what you mean by "life support" because strictly speaking, ANYTHING that is artificial that supports life can be considered "life support." This then will include a feeding tube.
To avoid confusion, I used the term "artificial treatment" since humans weren't able to keep people alive by implanting a tube directly into a patient's stomach before the past few decades.