I think you let them in, but it has to be noted somewhere about what went on during these years in baseball. I believe Barry Bonds knowingly used steroids, but he HAS hit more homeruns than anyone else in the history of Major League Baseball. Barry Bonds had a HOF career before he started taking steroids.
I think there is no doubt that A-Rod is an outstanding athlete, regardless of what he may have taken. McGwire and Sosa were known for their power, A-Rod for his versitility. I think you have to acknowledge what these players did, but there needs to be an "asterix", so to speak. I honestly don't see how any of the writers will actually ever vote them in, though.
Also, if any of the known steroids users are ever voted into the HOF, I don't know how anyone else feels, but I think Pete Rose should be in the HOF as well. Put him in at least as a player. They can still ban him from baseball and keep him from participating in the league and even ignore his years as a manager, but as a player he deserves to be in.