- When Luffy and others entered the scene of war at MF, Kizaru asked Sengoku if he could kill them all and Sengoku said none should be spared .
- Marines were already Bloodlusted after the killing of WB and removing as much pirates as they could.
- BBP were also going in action there while BB himself was ridiculously trying to destroy MF. There Sengoku and Garp took actions as well.
So Sengoku already ordered to kill all while he was also present.
Now when Shanks enters everyone stopped due to surprise. Later he even challenged everyone but none accepted. Kizaru asks to kill all when Luffy and other appeared but why not when Shanks came, why got his lips sealed even after hearing the challenge. There boss, Sengoku didn't got disappeared, he was present as well but remained silent till he heard Shanks conditions. Pirates attacking at the turf of there HQ while new emperor with his crew showed up, than for what reasons do even they need any permissions before engaging with them or missing glorious chance to remove as much as they can unless they felt been unprepared or inferiority.
Not even Kizaru's mouth opened after hearing Shanks challenge but even hot headed Akainu remains standing there like a statue.
Lol, no matter how hard you all try but you can't diminish Shanks position even a bit in the series.