Being realistic here, there are not many other serious contendors for interplanetary travel within a reasonably timeframe. When you take into account that interplanetary travel means your away from the safety of the Earth's magnetic field, being out in interplanetery space for any length of time is extremely hazardous and should be reduced if at all possible!
Ion drives and solar sails are very slow, chemical rockets require huge fuel reserves.
The nuclear alternatice, although undesirable in close proximity, is the only reasonable alternative within the bounds of current science theory. (Yes there are a few others like a mag-lev catapault etc, but they are not nearly as mature or as TESTED as nuclear).
Of course there are risks, but there are risks in everything. Look at the early colonisation of the America's and new diseases, look at the first sailors to venture beyond the ability to see land or the first transatlantic flights!
To live is to risk, yes this isn't just risking the lives of those going up there by those on the ground too, but this is where inteligent and transparent discussion should take place and the ideas should not be dismissed by the public/people because of the word 'nuclear' in it!
All science is advancement, its uses, for good or ill are determined by those who use it.
I'm hoping people will poke holes and retort because that challenges me to think and to elabroate on points! One should not accept things blindly, but too often people in general will do so, be swayed by the media and are not open minded at all (but those are topics for discussion elsewhere).