I'm fairly new to this, but my understanding is that molasses(sugar) only feeds the microbes in your tea, allowing them to multiply faster, not cause the growth of bad bacteria. What you want to be careful of is adding too much, causing your microbes to over-multiply and use up all the oxygen in your brew.

That is bad for reasons beyond my limited understanding at this point, but I'm sure a more knowledgeable soul will soon step in and put us both on the right path. :)