Fear triggers survival instinct.
Survival instincts are inherently selfish. We're not going to survive very long by stopping to let others go ahead of us when there's a hungry lion, tiger, bear, fire, angry leprechaun biting at our heels.
When we're afraid of getting hurt, of looking like an idiot, of being vulnerable, of losing the things we wish and hope for - we become selfish. Every man for himself.
If love is selfless, then fear is the opposite of Love.
Just a thought.