Hit them with bullet points that they will care about right at the start to grab their attention. Then explain why it matters.
"""
Dear <<WHOEVER>>,
I'm writing to inform you of a change that Google is proposing which will:
1. Reduce the ability of the security agencies to do their jobs
2. Limit the ability of ordinary citizen to access the internet
3. Lock control to big tech companies and reduce innovation in the technology sector
As a citizen of <<COUNTRY>> living and voting in <<REPLACE>> and a software engineer with X years of experience, I believe this proposal (called Web Environment Integrity or WEI), although presented as improving security and privacy, is damaging because ...
"""
Stress "anti-competitive"/"antitrust" perspective. For those in the US - an ancillary buzzword for some districts you could go as far as label this as "one further step towards <insert your flavor of "Communism"/"Socialism"/"Fascism", regardless if it actually applies or not(crony capitalism via favoritism is more apt but less likely to pique interest in said districts)>"
I tried to put it in language and terms anyone could understand while building up terminology. Maybe I need to rethink the audience.
In the emails I sent I did use judicious formatting. i.e. "Prevents alternative browsers" is in bold, and "this is anti-competitive" is italic so someone scrolling through it could just read those.
How it works could be dropped or pushed to the end.
Email messages go straight to staffers who might read it, but odds are it will go to the trash folder. Write a physical letter instead. Attend any "town hall" events and bring the issue up.
""" Dear <<WHOEVER>>,
I'm writing to inform you of a change that Google is proposing which will:
1. Reduce the ability of the security agencies to do their jobs
2. Limit the ability of ordinary citizen to access the internet
3. Lock control to big tech companies and reduce innovation in the technology sector
As a citizen of <<COUNTRY>> living and voting in <<REPLACE>> and a software engineer with X years of experience, I believe this proposal (called Web Environment Integrity or WEI), although presented as improving security and privacy, is damaging because ... """
(edit: formatting and expanded the final line)