Wow! One unfortunate shuttle accident involving a solid rocket booster (SRB) and the old Thiokol churn begins again.. Wouldn't hurt to get your facts straight Rudnric! While COTS is valuable and should be a NASA pursuit, scrapping the billions invested in ARES I would be stupid! If we are going to go any further than LEO we need heavy lift capability. The proposed ARES V is the answer but where do you think ARES V development has been taking place?  That's right! ARES I SRB development technology is directly transferrable to ARES V. Without ARES I, ARES V becomes more expensive. Since you're not the astronaut that will ride the light, you might want to ask them if they want to be the first to ride a COTS booster (Remember the first two Falcon I launch vehicles... poof!!) Since there have been no other SRB launch failures in the history of the shuttle program, and since the Defense Dept has launched hundreds of SRB ICBM's with complete success, the facts about the safety and reliabilty of SRB's is clear. If you are still a little hazy read on..

The ARES I SRM is safer as a first stage launch vehicle for many reasons. A few include:

1) Fewer moving parts- Other than the thrust vectoring the motor has no moving parts.
2) Safer handling- No liquid fuels. Ground handling is safer and inherent difficulties with liquid fueled motors such as high speed turbopumps, fuel pressurization, venting, and cooling are eliminated with a solid motor.
3) Although the early Challenger failure brought to light a design weakness in the early shuttle SRM, the engineers at Thiokol knew that launching Challenger on that fateful January day would exceed the design parameters for the O-rings. This information was given to Thiokol management prior to launch and could have avoided the disaster. Not wanting to be the cause of an expensive delay, Thiokol caved and authorized launch. Since the Challenger disaster, no additional mission failures can be attributed to the SRB.
4) Military ICBM variants of solid rocket motors have also proven safer, more reliable, and can stand on station for decades. The infrastructure to accomodate liquid fuels aboard a submarine or in a missle silo is eliminated.

Yes there are some disadvantages to solid motors.

1) The combustion process generates perclorates which are toxic.
2) Once they begin to burn, they can't be shut-off or throttled back. One exception is Burt Rutan's motor for SpaceShip One. Not designed for a heavy lift mission but a future application may be possible.
3) Higher vibration associated with SRM's.

The second stage liquid fueled motor for ARES makes sense because liquid motors have the advantage of being throttleable and can be stopped and restarted. As a first stage however, no liquid fueled rocket can compete with the safety and reliability of a SRM.

I'm a big NASA booster, and while they have definitely learned something from every failure, they have repeatedly and frequently not taken those lessons to heart, or only half-heartedly implemented those lessons, or with time they were forgotten.

If NASA were to allow astronauts to fly on a commercial ship, I do think they should be allowed to review every component and design decision, and veto the man-rating if they felt necessary. But I do think it is unwise for a private company to unquestionably follow NASA specs and requirements at a micro level. NASA just doesn't have the untarnished reputation to be expected to demand this. A private company should have an opportunity to prove out their own designs.