There was an awful lot of discussion about this after poisongate, so I hesitate to bring it up yet again. But I think something is still amiss.
I just poisoned my first two trees in my backyard so I could replace them with different varieties, which I did immediately following the decay. I was rewarded with -400 mood and 7 minutes of poisoner's guilt for doing basic yard work.
This has probably been suggested, but, when one plants a new tree, how about something to counter the massive mood hit and ensuing guilt buff? It's been my understanding that the devs want to stay as neutral as possible concerning good and bad behavior as it is reflected in the game mechanics. So in the spirit of balance, shouldn't planting a tree grant the player +200 mood and 7 minutes of Planter's Pride?