How important is identity protecton?

[=?gb2312?q?king=20wu?= <wmyking49@yahoo.com.cn>]

hi,all
    In IKE, how important is identity protecton?
    In IKEv1, only the main mode with public key
encrytion can protect identity of both sides from a
active attacker.However, the modes are removed in
IKEv2 and JFK. IKEv2 or JFKr just can protect
responser's identity from a active attacker. 
    In my opinion, we should protect a initiator's
indentity rather than a responser, because a responser
is usually stationary and its identity information can
be found more easily.
    However, the thing puzzles me is that for a active
attacker, will he acctack a link more easily if he
gets the identity information of one side or both. If
the answer is yes, then why not we try to protect the
identitis of both sides? 
    So, i have to ask,"how important is identity
protecton?" 
    please help,
    think you

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