The argument is like jedberg describes, if you have to disclose your trades far ahead of time, does having inside information matter? Make them plan far enough ahead that it's ineffective.

To me, the thing you are trying to curb is the short latency. You don't want, let's say...the head of the senate intelligence committee talking about how prepared america is for pandemics, and then turning around and selling a bunch equities. Or, calling his brother in law for less than a minute, directly after which he calls his broker.

Imo, it's the difference between, "disclose your plans, providing an opportunity for questions and looking for ethical red flags" and, "seeing the transactions after the fact, after which the people always say, 'nah, nah my guy, you got it all wrong, I already planned to make these trades, or it had nothing to do with the non-public information I had access to ;)"