Mandatory note that the AR-15 is just "Scary Black Gun" and that gun control efforts would be best served by focusing on features and accessories (and especially, actually fucking enforcing licensing and background checks) that actually increase lethality or mass-shooting potential of a gun.
... but the AR-15 fetishism by gun control opponents is cringe anyway.
First: need doesn't play into civil rights. You don't need to have freedom of speech, religion, etc. And yet, these are your rights as a legal resident of the US. (Note that 2A rights are also rights for any person that is a legal resident of the US, including student visa holders.) Would anyone support licensing requirements prior to voting, shitposting online, or not having your house searched by cops on a whim? For anyone that thinks 'features' bans are a good idea, here's the judicial argument against them. Short version: if you can ban everything except the 'gun', because of how a 'gun' has been defined under the law, you can functionally ban guns, which undermines the entire point of having a second amendment. Maybe you think that's good; I would say that the entire history of gun control in the US disagrees with you, as it has always been used as a bludgeon against the black, the immigrant, the working poor, and anyone that doesn't have wealth, power, and privilege.
Second: an AR-15 is useful because:
it's fully modular; you can easily customize it to suit your use-case. This is not true with most other rifles.
They're cheap, and so are parts. Because so many are made, you can pick up one that's perfectly serviceable for about $500. In contrast, my carry pistol (CZ Shadow 2 compact) has a retail of about $1300 for the gun alone, not including spare magazines, optics, replacement grips, trigger parts, barrel bushing, slide stop, IWB holster, etc. My AR-15, all in, with optics, trigger, multiple magazines, replacement barrel, muzzle brake, etc., cost less than my carry gun. A Glock 19 g5 MOS and optic would run about the same as an inexpensive AR-15 and red dot.
ammunition is cheap (for a rifle), and readily available almost anywhere. At about 40cpr, it's cheaper than nearly any other rifle ammunition.
You have fewer issues with over-penetration as a home-defense weapon; the bullet tends to start tumbling as soon as hits drywall, and quickly loses speed. 9mm can have bigger issues with over-penetration in a home than 5.56/.223.
It's more effective than a shotgun for home defense use, because it's more controllable, you have more shots before you need to reload, and it's easier/faster to reload. (Have you ever seen someone doing quad reloads on a shotgun? That's a skill that takes a very, very long time to master.) No, you don't have to just point a shotgun in the general direction of something; at home-defense ranges, shot spread is negligible. Most shotguns will also be longer than an AR-15, which make them less-ideal for more confined spaces.
It's more effective than a handgun; a longer sight radius combined with more points of contact on your body makes it easier to aim and shoot effectively. And, again, you have more ammunition, which is a good thing when you're feeling deeply stressed. (Would an SBR AR-15 or a bullpup rifle be even better indoors? Yes.)
They can be incredibly accurate; it's not difficult to turn an AR-15 into a sub-MOA rifle. A Ruger Mini-14 will never do better than about 2.5MOA.
It can easily be chambered for multiple cartridges by swapping out barrels. With a different barrel, you can use a large variety of different cartridges, the most popular of which are .300BO, 6mm ARC, .400 Legend, .458 SOCOM, and .50 Beowulf.
Plastic and aluminum pieces are less susceptible to environmental issues, e.g., they aren't affected by humidity and rot the way that wood is.
As far as the so-called "fetishism" goes - it's a tool. It's an effective tool, and often the best tool available. It's also an ad hominem attack; it says nothing about the tool, and instead goes after the people.
Cringe.