Draco's not really evil,he's a bully and we all know that bullies are cowards

.If Snape hadn't arrived,I dont think that Draco would have killed Dumbledore

.Anyway,since his parents support Voldemort,so automatically he too supports them.This is natural in most cases,with some exceptions like Sirius Black.But,I dont think he's got the guts to support Harry and confront Voldemort.