I'd have to agree with Ranger.
Those guys that planted on your property? Oh yeah, thats yours all day...I mean they are placing you and your family at risk law-wise, so like NDW4M said, they're lucky to just have you take 'em.
But out in some field, woods, or ditch, or anywhere else public?
I mean, you have to ask yourself how you felt, feel or would feel every time you raise seeds from start to finish and suffer right along with the plants, thru pests, burn, environment, sexing excitement, harvest, etc. And knowin' all of that and what work, passion etc goes into cultivation of MJ, and also knowing that our own US govt oppresses ALL OF us and is fighting a war against us each day, and destroys and confiscates it every day of the week, why would you then join in that war against a fellow grower?????????
People who consume herb in its various ways and understand the usefulness of the cannabis plant in general, in my opinion, should hold themselves to a different standard than those who refuse to educate themselves about green. Our conscious is "elevated," after all. And someone who grows, of all people, should most definitely be able to appreciate the significance of someone else's guerilla garden and what that means, as well as what that person must be goin through.
And whether or not someone is regularly tending to them or why someone might be "stupid" enough to plant em there really is irrelevant, from an honor standpoint. Thats when your integrity should tell you to look and analyze yourself, NOT their decision to put it there.
If their stupidity or lack of attention to the plants outweighs your concept of taking from someone that YOU KNOW is fighting in the same struggle as you, then that gives us a pretty good idea of how much weight your values carried in the first place.
Not directed at anybody, but.....for anybody
Peace
I'd get more satisfaction growing from seed anyway. And, it might give RangerD some relief that I won't rob the Highway weed bank 
