I disagree with this perspective for many of the reasons outlined in this comment (on a thread about registering with the Labour party for similar reasons). I think it’s good if EA action, political or otherwise, is taken in the spirit of cooperation and honesty, and registering for a party whose positions you broadly oppose doesn’t seem to follow that.
(There are exceptions to this principle, of course, but given the relatively low impact of voting in statewide or national elections, that doesn’t seem like an exception worth making.)
Maybe you could choose to only vote in a party’s primary if you also precommit to voting for your chosen candidate in the general election if they win the primary.
Strongly agree that we should be cooperative in general.
On my Facebook there’s extensive discussion about whether registering as Republican is cooperative or not (one big difference here is that party registration seems meaningfully different in the US and UK, eg, in the US there’s no dues).
Personally I will strongly recommend against registering for a party unless you want to think of yourself as belonging to that party, potentially for years or longer.