About the morality issue: I feel you, I believe this kind of sadness comes from our tendency to humanize non human creatures.
So, as we wouldn't like to be locked in, we perceive it as horrible for a plant as well, while we're completely ok in seeing flowers in a pot, for example.
The fact is that the plant in a jar (if it's done properly so that you allow an ecosystem to be created) is self sufficient and in balance with the existing microfauna. They have everything they need, that is food, air, water, sun, without human intervention. While the plant in the pot will always need your intervention to survive and, unless you periodically add compost or nutrients, keep it moist and shaded, the soil will die and the microfauna living in it will die with it.
Now we are talking about morality issues, so I believe there is no right or wrong. I just wanted to share with you my personal view about this