I wonder why did so many people support the Equalists. I and my mother discussed "why do what kind of people support the Equalists?" yesterday.
My opinion was as below;
"There are non-benders who have bender(s) as their family (e.g. Haru's mother). Will such a people support an organisation like the Equalists despite they're supposed to bring fear to benders? I think that benders aren't a minority nor an overwhelming majority. If benders are an overwhelming majority, the Equalists will never be supported. Perhaps non-benders are many in their own way?"
A) Statistically speaking, benders are the minority, you can go back and look at early text that confirms this.
B) Even so, I do think that it's likely an organization like the equalists would still be supported. The Equalists, as they presented themselves for a majority of the show, are interested in creating equality through the elimination of bending. If your son has bending, but let's say you've also seen benders use their abilities to cause severe harm to others, it does not sound like removing his bending would be terrible. In addition, Amon initially presented his goal as removing the bending of "bad" people. Which, looking at the results, isn't something even Avatar Korra or the city disagreed with since they kept the triad members bending removed.
Bryan Konietzko explains it here. Actually, in the same talk, but early in Part 1, he mentioned that the "militant Equalist" subplot probably wasn't going to come back. So not everyone who identified with the Equalists was dressing up in black jumpsuits & demanding for benders to have their powers taken away. Those who had close friends & families who were benders were probably less likely to do that.
To add to what Bryan says, you see a lot of problems in Book 1. The Council, at the time, is entirely composed of benders, who are even willing to push discriminatory laws onto nonbenders. We see Tarrlok, & even to some extent Korra, abusing her powers with impunity. The whole field of Pro-Bending is impossible to break into if you're not a bender, & other jobs are at least preferential to benders, such as the power plant workers who all generated lightning--something we're told "pays pretty well," despite essentially consisting of standing around pointing at a generator. Then of course there were the bending triads.
Well, just looking at the two series, the only one of the original four nations that was composed entirely of Benders were the original Air Nomads. Based on what we see of the others(and I think this is addressed in an official source of some kind), the population of the Earth Kingdom is overwhelmingly composed of non-benders, with benders being a very small minority.
As for the Water Tribes, well we know that as of AG 100, the total population of benders in the Southern Water Tribe is precisely one individual, with the entirety of the rest of the population being non-benders. As for the Fire Nation and the Northern Water Tribe, both have substantially larger populations of benders, but still seem to have a large number of non-benders as well.
As for the URN, IIRC LoK Book 1 heavily implies that it has a very large nonbender population. I have three main reasons for this:
(1) The massive size of the Equalist movement implies two things: A lot of funding, and a lot of manpower. Both require very substantial popular support. Even setting aside the fact that their tech was bankrolled and provided by Hiroshi Sato, if we assume they had no other source of income(which I deem unlikely), that still leaves the problem of manpower - and you saw how massive the crowd was at the Equalist rallies, plus the fact that even if we assume that fanatically militant anti-benders are only a small percentage of the Equalists' supporters, there were enough of them to assemble what amounts to a small private army. Thus the overall pool of people who support the general ideals publicly advocated by the Equalists is probably extremely large, which can only be justifiable if there is an extremely large population of non-benders.
(2) Following the dissolution of the Council, the first democratically-elected leader of the URN is a non-bender.
(3) While the URN's mixed population means that it probably has a statistically higher percentage of benders, the fact remains that its original population - as a former Fire Nation colony - consisted of a Fire Nation upper class and an Earth Kingdom lower class, the latter of which statistically probably included a majority of non-benders(See The Rift).
To me this means that it's a safe assumption that the vast majority of the URN's population is composed of non-benders.
It's addressed in at least one official source that I named a little while ago. I'd have to dig deeper into the original series to say if you can tell just from onscreen characters, & I don't wanna. I know there are a lot of places where it's confirmed that there are only a few benders, but a lot of these were specifically purged by the Fire Nation.
To reply the OP, the kind of people who accepted fascism, the alt-right or communism. A simple resolution to their nation's (and the world's problems) is offered by a charismatic leader who seems to have the power to solve this problem for the first time in forever.
Remember, Amon suggested that benders caused all the wars in history; The Triads are made of benders at this point; the police's main force are metalbenders; although society is divided politically by cultural/national bounds but in the metropolitan Republic city this almost looks like division by bending type; and I'm willing to bet that many benders are in positions of power and wealth due to ancestoral duties/working efficently in areas where bending helps. Now all of these aren't really based on bending, but they look like it if your a non-bender and down on your luck. Surely everything would be a better for you - a more peaceful, prosperous and powerful life - if benders weren't in the way.
Also Amon claimed his mission was from the spirits themselves, this adds a huge amount of authority to his claims - most people don't have experience with spirits and this power that isn't obviously bending, so maybe this is a sign for the future of humanity. Espcially since the other main link with the spirits is the Avatar, who is not only a power holding bender but the current one has made no obvious proof of favour of the spirits. So maybe they back up the equalist ideals.