Is rinsing your mouth with hydrogen paroxide a bad idea for whitening teeth? If so what are the side effects?

Won't do much and.. Rinsing with hydrogen peroxide in the concentration available to you won't whiten your teeth. Rinsing with hydrogen peroxide on a regular basis is not a good idea as it may irritate the soft tissues of your mouth and cause other issues. If you want to have whiter teeth, consult with your dentist who can discuss the available methods and what would be best in your particular case.
Different peroxides. Tooth bleaching substances are made from carbamide peroxide which is different than hydrogen peroxide. The latter is a potent oxidant that is useful when diluted for a small number of intra-oral issues. Carbamide peroxide is the active ingredient in dental bleaches and is much safer to use.
Bad idea. To whiten your teeth, you havta have contact with the bleaching agent (perixide) to your teeth for 1/2 an hour or more at a time. Rinsing with peroxide for 1/2 hour will cause your gums and mucosal tissues to become raw. Don't do it! to bleach your teeth, you need to minimize the contact of the peroxide with the gums and mucosal tissue. Good luck!
Hydrogen Peroxide... Hydrogen peroxide is an oxidizing (oxygen producing) chemical that can kill many bacteria but not touch other organisms such as Candida Albicans which then causes a super infection or thrush resulting in a raw, sore tongue and cracks in the corner of the mouth. Therefore use it once every other or third day to enable the ecology of your mouth to get back to a normal balance.