Let's see -- in 4 decades of American space missions we've had three fatal situations, and one of those was on the ground. There's a real enough risk, though we've worked to reduce it (look at the Soviet space program for comparison) but *nobody* is being forced to take it; it's hard enough to get selected. I say we continue.
The biggest threat to our space program is not the infrequent accident/tragedy -- it's the bureacracy for a LONG time now firmly entrenched in NASA, soaking up the dollars and slowing any development in progress. What was it, eight (8) years from the inception of the Mercury program through Gemini into Apollo and the lunar landings? We have much more advanced technologies today, but I doubt today's NASA could repeat that feat.
(It's been 30 years since a NASA researcher in my department told me, morosely, that they had passed the milestone of "one bureaucrat per scientist.")
Watch as they add even more management after the latest tragedy.