Raccoons are most noted for carrying the rabies virus, however they are known to carry other diseases also. These diseases are not only transferrable to other animals, but can be contracted to humans as well. The most commonly spread is roundworm, of which the eggs are excreted through the waste of the raccoon. These eggs may be airborne, and are capable of being inhaled - which increases the potential harm to humans. They also are known for spreading leptospirosis, also carried in their waste. This requires direct contact with the waste in order to be contracted, which is why you should always wear protective gloves when coming into contact with raccoons or their waste.
There are other risks that come from raccoons living in your attic, although not disease related. Raccoons will destroy your attic once they are inside; they will rip insulation, scratch and potentially break beams, and cause damage to the AC ducts. These can not only put your home at risk, but can end up becoming quite costly to repair. Raccoons will also chew on electrical wiring, which can put your loved ones at risk by creating a fire hazard.
Raccoons are cute to look at, however, once they are in your home they are a risk to your livelihood. These risks are some of the main reasons that as soon as a raccoon problem is noticed you should be taking steps to eradicate it.