I am setting out to make plum jam from some edible wild plums growing in our backyard. I found one recipe that calls for pectin and 7 cups of sugar, which seems like a lot of sugar. I've also found several recipes that call for half the sugar and no pectin.

Would it be bad (i.e. will someone get poisoned) if I use less sugar? If I reduce the sugar, will it not need the pectin?