Yes, I don't have to kill them, but they tend to die nevertheless in this process. While flower can survive without its roots, there is going to be a lack of necessary minerals to keep it alive long term unless the care keeper is really, and I mean REALLY good. Hence the comment on terminal patient, taking a flower without its roots is pretty much equivalent to having a terminal patient in your living room. It's alive, but there's no turning back and I have inferred in the natural life cycle of a plant, possibly killing it before it could reach any kind of maturity without any sort of reason.
For some reason, women don't prefer potted plants on the dates - when given a chance, I prefer to take them to gardens, there the plants are at least alive and tend to remain so.
I'm a born romantic, aren't I?

EDIT:
you're actually tearing off the plant's reproductive organs and displaying them as a trophy
EDIT^2:
Actually, it is part reproductive organ, and partially required for photosynthesis, without it, the plant will die as well. So it's not only a reproductive organ.
Haha! Never thought it that way, but that's usually true as well! Let me try to put that in more understandable terms: the root is not sufficient for sustained plant life, leaves are the key for the photosynthesis and that is a required condition for sustained plant life. So it is not only a reproductive organ that you are decorating your living room with.