Secondly, because of these common commitments, a degree of shared history and therefore identity is formed much more quickly and strongly than in non-alliance organisations. Common trials and common enemies bring a sense of unity.
Are there other sufficiently effective ways to build community and unity without having to deal with negative side effects of alliances?
And above all, they are an expression of the basic human spirit of cooperation and tribalism that surely has its place in this sandbox of ours.
Tribalism definitely occurs in any game but by grouping players into alliances we are almost forcing players to play the game in the confines of an alliance or play with a massive disadvantage to others who have the benefits you described above.
For context I voted neutral but would like to have follow up discussions about ways to increase the benefits but counter the negative aspects of alliances.