The question was along the lines of what to do when something as lovely and beneficial (to plants, animals and humans) as the comfrey plant decides to take over your garden and reproduce like an alien invasion? Comfrey, apparently, can be boon or bane!
A quickie internet excursion took me on pleasant trails in quest of an answer to this dilemma. Depending upon the variety in question, if you have hundreds of wee comfrey plants peeking up from your garden soil, it's clear they are of a type which seeds themselves with wild abandon.
The conclusions I found from my foray online was
a. Nevernonevernonever rototill the little guys under. Doing so would chop those roots into bits that would THRIVE on reproducing ever more comfrey ad infinitum
b. Always keep these plants in containers or a contained bed
c. If trying to remove, do NOT cut them at the root, and DO sift the soil to remove all roots
OR (and there are varying opinions on this)
d. Put a chicken tractor or portable electric fencing around the area and let chickens, turkeys, ducks, or geese go to town. Chickens will eat all the comfrey AND, if left long enough to dig and scratch, will supposedly even eat all the roots. The caveat in all this is the literature out there that questions the healthfulness of comfrey when ingested by poultry. There is other traditional opinion that it's perfectly healthy for poultry, but critics claim it has a toxicity that can produce liver damage when ingested in large quantities.
Supposedly, there is no way to eradicate them unless you try #6. However, (do not lose hope!) #6 has been tried (and has succeeded).
For more on this, see this fascinating article, "Feeding the Flock from the Homestead's Own Resources" at the link I'm about to give. In fact, this site has great information on growing some easy, beautiful, and beneficial sources of poultry feed:
Can't offer anything here from personal experience, but filing this info away never hurts. And don't be scared away from comfrey...its advantages surely are numerous, and it's said to increase the vigor of many plants. And, though stinky, a "garden tea" made from its leaves is said to be a great fertilizer!