Which MP was it?

I also wrote specifically on just cage free hens last year here:

https://forum.effectivealtruism.org/posts/soz6CerTGpEWFXLeZ/is-cage-free-really-the-most-humane-option-for-egg-laying

There are some responses from the Animal Welfare Project team in the comments there that respond directly to some of the overlapping points.

I can't speak to this specific case, but speaking generally, debit and/or credit card transactions can incur flat fee, making small donations not cost effective, especially if the card is in a foreign currency.

A sufficiently small donation can actually cost the organisation money, so it's very common to set a minimum donation amount. $5/£5 is likely safely north of that amount, but because fees can be variable, you do want to leave some padding in.

Minor editorial correction:

Okay, technically fish are a swing species in that there isn’t complete agreement, but there’s a pretty broad consensus.

I would say "group" rather than "species" here (since fish aren't even a valid taxonomic group, let alone species.)

Since fish are vertebrates, I think the certainty is much higher than invertebrates in general. For invertebrates I am not convinced.

If invertebrates were conscious, it'd be very bad. For one, vertebrates typically lose consciousness very quickly when they sustain fatal wounds, due to blood loss which causes the brain to lose oxygen.

Most invertebrates' nervous system is passively oxygenated. That means the brain keeps working long past the time when the rest of the body dies... even ex situ. It's why invertebrates are used for studying neurophysiology, both because the neurons are so large compared to vertebrate neurons, and also because neural tissue continues to function after death.

If true, the wild animal suffering implications would be enormous.

Should be "its" not "it's".

I'm curious whether you've indicated parental care is "present" or "absent" in bees, however, I have briefly checked the documents linked and couldn't find where that lives but maybe I missed it. Can anyone link to that documentation?

(Bees provide care to young, but it's primarily done by siblings, not parents, so it's considered alloparental care, not parental care. I should think that probably counts, but wasn't sure.)

It is not uncommon, and I will even say usual, that Nazi sympathisers are at least somewhat subtle about it.

This is not particularly subtle. Here's their section on the Holocaust: https://nyadagbladet.se/tag/forintelsen/

Here's an editorial written for Holocaust Remembrance Day. Their central claim is that the way to prevent antisemitism it to stop "lying" about how many Jews were killed. https://nyadagbladet.se/ledare/sa-forebygger-vi-den-verkliga-antisemitismen/

This is very classic Holocaust denialism. I don't think it's unreasonable to call a website that actively promotes ethnonationalism and Holocaust denialism "pro-Nazi", unless you think that the literal words "pro-Nazi" must appear somewhere in order to qualify.

Good post, though I should point out that HIV entered the human population independently at least twice (HIV-1 and HIV-2), so your counterfactual world missing HIV might not be as likely as one might otherwise think.

(There are also counterfactual worlds where SARS-CoV-1 or MERS-CoV or similar took off as well with an even higher death count.)