not "bad" per se. i have field collected moss, but i cleaned it thoroughly, then gave it a very mild bleach dip, followed by an even milder peroxide dip. problem with field collected moss is the little nasties that tag along with it. now this only works for aquatic moss. for terrestrial mosses, i would grow them out in a separate container for a couple weeks to see what else grows in there. a tupperware container with a little soil would do the trick nicely. here's how i grow moss. in tupperware, utilizing my fish tank lights. this is aquatic moss i am growing for the mantella tank: