I'm going to be the contrary one and devil's avocado all at once and say I think this is a great idea.
The OP made no reference to representing this website anywhere, and also made it quite clear that hindering doorways, etc, is illegal, and so on. I think they have acted quite responsibly, really, in the way they've put this across.
I think it's a good day to get attention for the plight of the betta. The OP was not suggesting outrageous or aggressive behaviour - if you actually read the post, they are stating the exact opposite!
I too am a veteran protester, and in the past have actually chained myself to things (back in the days when we had more civil liberties/guts/a voice) including trees and a train station to try to get people to become more aware of wrongness occurring in their community. I've also done peaceful sit-ins, park gatherings and flag burnings (I am not recommending anyone do that, ofc - just things I did in my wild youth..).
In my experience, protest does make a difference - but only if it's respectful and peaceful.
That's why PETA are pooh-poohed as raving loonies (aside from the fact that a good number of them actually are raving loonies in an organisation that kills animals to make its point, yeesh) - those guys go for shock/anger as a platform that gets people offside from the get-go.
Anyhow, I don't see anything irresponsible or disrespectful going on here at all. I hope those who do have the courage to protest peacefully at Walmart have a great and very positive day and come home with a smile.