Why didn't Allen just kill Makarov at the start of No Russian?

I have never understood this seemingly major plot hole in this mission. We know a few things:

• Allen is an undercover spy posing as Alexei Borodin, in order to figure out what Makarov is up to
• Makarov and his cohorts already planned to shoot up a Russian airport. This would've been enough in my opinion to kill Makarov -- what is there to uncover if it is already crystal clear he plans on massacring civilians?
• Perhaps Makarov is up to something much grander -- but killing off Makarov would ultimately delay or ruin those future plans, and at this point it's clear how many countries want Makarov dead.
• We know that Shephard betrayed Allen by revealing his true identity to Makarov - We know that Shephard intended on Makarov to kill Allen to spark anger between the Russians and the US, but Makarov doesn't take action UNTIL they are about to escape, as opposed to Makarov knowing that Yuri betrayed him and leaving him for dead PRIOR to the start of the mission.

Thus my question is, why didn't Allen just kill Makarov at the start of No Russian?

Solution 1:

This is widely considered to be a plot hole, along with the Russian government using one American corpse as evidence of the attack being an American plot, rather than using on-site cameras to identify the actual Russian perpetrators. There, frankly, isn't a valid reason why Pvt. Allen doesn't kill Makarov in the elevator before the massacre.

But with that being said, there are some fan theories that may explain Allen's decision:

"Shepard probably ordered Allen not to take out Makarov. Shepard was probably planning for Allen to get killed, and wanted Russia to invade the US. This is because if Russia was the aggressor, America would have the public's support and so Shepard could re-attack and destroy Russia. Shepard was in cahoots with Makarov, that's why he wanted the intel from Makarov's safehouse. If he had it, no one could discover he was behind it all. It was all a plot conceived by Shepard so that he could go to war with and (possibly) defeat Russia."