Although an even bigger problem is the SRBs are, in fact, solid rocket boosters. Solid rockets can't be controlled in-fligh; they burn until they're out (the SRB thrust is actually modulated in-flight by the changing shape of the central cavity in the solid fuel, which increases or decreases the burn rate - so it's actually pre-defined and fixed). At any point in flight after the SRBs, the shuttle engines can be powered down (or up, sometimes) in case of an emergency. While the SRBs are burning, it's "Ride it until they're done, and God help you if something goes wrong." For that reason alone, crew evac is virtually impossible from a rising shuttle.
Those are also the only solid rockets in history to be man-rated, for the simple reason that the thrust is uncontrollable real-time. Even the Soviets, with their greater willingness to take casualties, never man-rated a solid rocket.
They'd have to be. And that in itself says volumes about how badly managed the shuttle program has been. Had the SSMEs been properly engineered from the start, they wouldn't need to be completely different engines now. Instead, they still had unexplained failure modes on the shuttle's 60th "operational" flight and beyond.
And in saying the SSME's were "1980's era", I meant that they were at the time of design. They unquestionably pushed the state-of-the-art well beyond where it was at the time; one could make an excellent argument that they pushed it far too far. One rarely manages to combine "bleeding edge" with "high reliability" in engineering, particularly when engineering practices as God-awfully horrible as how the SSME project was managed are applied.