Why did Ambassador Jeffrey Sinclair not want Garibaldi to join him and others on War Without End mission?

Question

In the episode "War Without End":

Jeffrey Sinclair, Commander Ivanova, Ambassador Delenn, Marcus and Captain Sheridan travel back in time to Babylon 4.

I did not understand the reasoning explained in a scene explained by Jeffrey Sinclair to Garibaldi at all.

In the scene, Jeffrey Sinclair left Garibaldi a private voice message, stating he did not tell Garibaldi he was on Babylon 5 because Jeffrey believed that Garibaldi would either try to stop him or join him on the mission.

However..

Commander Ivanova was allowed to go on the mission and she was equally as important in the timeline as Garibaldi was.

What was the reasoning behind Jeffrey Sinclair not wanting Mike Garibaldi to not join them on the War Without End mission?

Answer 1

If memory serves, Sinclair didn't want Garibaldi to follow him because Garibaldi also traveled with Sinclair to Babylon 4 in Babylon Squared, back in the first season, while Ivanova did not.

So Garibaldi would not have survived another trip there and back through the time field, or at the very least he would have aged like Sinclair did, since both of them were previously exposed to it without any protection.

Answer 2

Garibaldi would have insisted on not only going with, but also on staying with Sinclair throughout the mission.

Since the mission was, for Sinclair, to go back in time and become Valen, and Valen arrived alone, Sinclair could not risk Garibaldi going back with and altering the nature of the Minbari. Further, Garibaldi would not be able to fit in to Minbari society even if altered to look Minbari.

Plus, there's also

the aging issue. Garibaldi had spent as much, if not more, time in the time field during the first appearance. A return trip would have been as hard, if not harder, on Garibaldi, than it would be for Sinclair.

And also, the issue of Michael being prone to act first and think later...

Michael would likely have KO'd Sinclair to "save" him, and would have made a very poor Valen. And might not have been able to make the transition to being Minbari. We know Sinclair is strong in whatever it is that makes the transition possible, because the Triluminary lit up for him. We don't know that Garibaldi is.

Bringing Michael Garibaldi is a risk to the mission on just too many levels.