Vaccines.Procon.org – Our popular website on the mandatory vaccine debate has been updated and expanded with new pros, cons, background, and did you know? information, with over 130 sources cited. Proponents of mandated vaccination for children say that vaccines are safe and one of the greatest health developments of the 20th century. Opponents say that vaccine ingredients are questionable and vaccines cause serious, and sometimes deadly, side effects. Explore both sides and decide for yourself.