Is there anyway to convince Zelazny to stand down?

Solution 1:

According to the wiki, you can't reason with the guy. He's just too darn stubborn, and reasoning will only make him fight you.

You CAN, however, decide to approve of his actions, side with him, and then later lie to Dr. Wing about what happened, and you'll still get the quest reward.

Source: Wikia: Talion A.D. page

Solution 2:

As Artless said, you can't reason with him. However, you don't have to kill him. A gas grenade is a particularly effective way of taking him and his men down non-lethally.

Solution 3:

In addition to Artless's answer, you do not have to lie to Dr. Wing in order to complete this quest and get the Praxis kit, simply tell him the truth and use the 'convince'* option.

**I have the 'social enhancer' augmentation and do not know if it is required for this option to be available*