OK, I'm gonna try to clear this up for everyone....here goes, this is straight out of the cervantes indoor/outdoor growers bible. I can't cut and paste due to it being a pdf. So here it is.
HYDROGEN PEROXIDE
Hydrogen peroxide is similar to water but carries an extra, unstable , oygen molecule which can break down into a reactive atom and either attach itself to another oxygen atom or attack an organic molecule.
Used in horticulture, hydrogen peroxide provides a host of benefits by cleansing water of harmful substances such as spores, dead organic material, and disease-causing organisms while preventing new infections from occurring. It removes the methane and organic sulfates often found in well water as well as removing chlorine from tap water.
Hydrogen peroxide is especially useful in hydroponics, where overwatering can be a problem. It prevents oxygen depletion in the water around the roots, leading to better root growth. A solution of hydrogen peroxide can be used to sterilize seeds resulting in better germination rates.
Hydrogen peroxide is dangerous at high concentrations (35%) and will damage skin, clothing, and most anything it contacts. Lower concentrations like those found at the drug store (3%) will still need to be diluted before use, though they are not as toxic to the gardener.
Maybe this will clear up the whole hydrogen peroxide is bad/good deal. and like i said i just retyped this straight from the book. so i cant take all the credit.