As envisioned, the six-engined XB-70 Valkyrie could cruise for thousands of miles at Mach 3+ while flying at 70,000 feet (21,000 m) – which was meant to make it practically immune to interceptor aircraft.

Aircraft, perhaps. AA rockets probably not so much. Huge radar and ir target. Isn’t real maneuverable at that speed.

What's to fear? What's the advantage of a manned bomber over missiles which are as effective and a lot cheaper and don't risk pilots' lives?

19fortyfive.com being as sensationalist as usual.