In their original, first generation state, Plants are fragile and cannot survive for long without their tank or bulb to contain them.
However, Plants in their Independent form are the ultimate invasive species. All strength, no weakness—the only flaw of the Plant is that once they are depleted of power, they die, and unless they expend all of their power and attempt to press further, their lifespans are unlimited.
Considering the potential for conversion or the birthing of future generations, once a single Independent hits the soil, the potential for full mass-species take-over essentially runs on a countdown clock.
Of course, as the Eye of Michael sees it, the Plants are the ultimate species. They don’t need food or water, so famine becomes a thing of the past. They don’t succumb to disease either. Essential, all suffering becomes a thing of the past, so long as conversions continue to take place.
If said conversions expand to take over the biosphere, while alternating in physical appearance, all species will cease to exist but Plants. The biosphere will have completely imploded, collapsing into an end of all strife.
Consider once discovering the ability to convert, the choices in Vash’s hands whether to let the his friends die, essentially leaving himself to the company of his brother for all eternity, or to potentially kickstart the end of all terran life by saving them. Technically all consciousnesses are preserved, but aren’t there still problems in this idea?
Chew on that. Where is your ethical god now?