You can ignore diplomacy in Alpha Centauri, but you miss a lot of the game's
flavor if you do. Plus, if you keep your reputation unsullied, you can gain a
lot of favors later in the game. For example, I made a point in my last game
in which I was playing the University faction) to ruthlessly secure my borders
and to placate everyone else.
I first got Morgan on my side by using a Free Market economy (money talks) and
then set up a trade agreement with him. The Techs I gained from Morgan helped
me to crush Santiago's faction. Meanwhile, I kept giving Tech gifts to the
Gaians to keep them fairly neutral. As a result, when I changed over to Green
economy, the Gaians, nearly rhapsodic over my environmental savvy and
generally magnanimous nature, signed a Blood Pact with me.
But I didn't stop there. I kept on giving gifts of Tech and Energy to keep the
Gaians happy. When they needed help against the Hive and the Lord's Believers,
I lustily sent my forces off to war (I never liked either of the sanctimonious
bastards, anyway). My benefits from this included the following:
The Gaians sent me more than a dozen military units to help "defend my
borders" against the Hive.
I liberated a Gaian base and gave it back to the rightful owner. In return,
Lady Deirdre gave me a captured Believer base on my border.
I managed to convince the Morganites to call off a vendetta against the
Gaians, which freed up Gaian forces to concentrate on the Believers.
The Gaians and I combined our research and lapped the Hive's Tech efforts,
which was ultimately why I won the game.
You can never be too nice. In Alpha Centauri, your former enemy may eventually
turn out to be your best friend strange bedfellows and all that (if this
concept confuses you, just think of the French).