Let n = the number of people whose lives your writing has effected.
Let m = the average magnitude of that effect.
Let e = the distribution effect of your medium (for one on one, e = 1,in a room of others, e = 2, print, e = 3, popular blog or forum, e = 4, etc.)
Let z = the sum of all the negativity of those who don't matter.
Then if the net total effect of your writing is A, we can say:
A = (n*m)**e - z
So, for almost any value of z, A will remain positive. Keep on writing. Please.