Why mobilize for the twin goals of increasing the personal exemption to the US federal income tax and creating a "FICA floor?" There are lots of good reasons, but those reasons will vary from person to person. These goals appeal to thinking Americans of every political persuasion.
Progressives oppose "regressive" taxation -- taxation that falls more heavily on the poor than on the rich. Increasing the personal exemption and creating a FICA floor makes the tax system more "progressive" and improves the lives of the poorest among us.
Conservatives and Moderates prefer lower taxes on balance and dislike sudden, novel, willy-nilly changes to existing institutions. Instead of a new, different, untested tax system, why not use existing tools to improve the existing system? The federal income tax -- which has been in place for more than a century -- already includes a "personal exemption" and Congress has acted to increase that exemption many times over the years. Our program would merely make that process recurring and automatic, and implement it with respect to Social Security and Medicare taxes as well.
Libertarians hate taxes in general and on principle and want to reduce and/or abolish them. Increasing the personal exemption and creating a FICA floor gives everyone who pays taxes a tax cut and removes the poorest Americans from the tax rolls altogether. What's not to like?
If one drew a Venn diagram of major American political groupings, these two goals would appear in the overlapping space representing ideas that are common -- or at least acceptable -- to most if not all of them.
We may not agree on anything else. We may not agree on why we agree with these proposals. We may not agree on where (or whether) to cut spending to "pay for" these proposals. But we agree with the proposals themselves. And that's what makes the proposals possible to implement. Enough of us agree that we can bring substantial public pressure on public officials and political candidates to endorse, support, sponsor and vote for the enabling legislation. So let's do that!