Well, I suppose the good news is that this might change somewhat with Utopia.
Apart from that:
As long as you play a non-fanatic pacifist, your ability to wage wars isn't really that much impaired. Sure, you have to diplo-vassalize + annex the liberated empires, but that is nothing stopping you getting a dominant position in the galaxy eventually.
As a fanatic pacifist - well, I'd argue they *really* should be against war. The fact that you lose your happiness in defensive wars (at least last time I played them) is quite annoying - but, again, that is known and may be tweaked in the future.
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