Anybody interested in legislation should be more careful about language use and - especially!- assumptions. Whereever you “heard” this, it’s inaccurate.
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There is nothing wrong or even problematic about putting down any (legal) political activities- for any school. You are who you are and you want to go to a school that values that.
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“Writing about” a topic is for essays, not for listing ECs. For all essays, the official “topic” is notional- the actual heart of every.single.essay is a showcase for you and why you are a great addition to the campus. So, if you are writing about being involved in writing legislation, it doesn’t matter what kind - it matters why you are doing what you are doing, how you got to a place where you are doing it, where you going with it next, etc. Writing an essay that is a polemic on why you believe in X or are opposed to Y is a bad idea because that’s not what a college application essay is for.
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Unless you single handedly wrote and passed the bill in question, you did not “write” legislation. You may have been involved in drafting it, but it’s unlikely your contribution went farther than that.