So, Sidewinders and Stingers and its Soviet and European counterparts, of generations predating the AIM-9X models... they use IR sensors, but not cameras.

They have a miniature Schmidt-Cassegrain telescope, and a rotary coded aperture, and a singular or just handful of gas-cooled IR detector devices. Either the aperture, or more commonly the entire telescope, is on a spindle and rotates at high RPM. So imagine one of those palm sized super long focal length camera lens is put onto a disassembled hard drive and the entire thing spinning at the disk drive speed. On models after AIM-9B, either the front group, or again the entire thing, is on a quick responding 2-axis gimbal.

A dot of heat source within view of the seeker, interfering with spinning coded aperture, will create a characteristic pulses and/or beats. The pattern can be half-open half-close disc, an asterisk/sunburst pattern, or a half covered asterisk. And the spindle can be strategically angled, or it can be perfectly straight. Anyhow, the way IR source is interrupted gives the seeker theta and alpha angles by the intervals of the blocker part of aperture passing over it, or the delay between the start of new rotation to the IR spike getting through and whatnot.

(I think this mechanism is where the hallmark Sidewinder grrrrr -> wheeeEeEeEEEEE growl comes from but I don't know...)

A separate flare sensor with filters to mask engine exhaust and focusing on flare spectrum is added, and it is wired to activate a mechanical aperture to limit the view as well as tracking disable signal to the seeker so that the missile flies towards last known direction as long as a flare is in the field of view of the seeker; the field of view is limited to a very narrow cone in the first place, and that is why seekers are built on the Schmidt-Cassegrain system, and extremely rapid tracking allows the seeker to work despite tiny FOV.

And, you know, in this day and age, it could be just a camera. And they in fact use cameras since AIM-9X and on(9X3? 9X4?).

And my point is, the US already uses the GP's suggested strategy of maintaining bare minimum military spending at uneconomical price to be spent on maintaining emergency ramp-up capability, combined with regularly repeated and easily won wars in Central Asia, as well as strict controls of advanced military technologies such as what I described above to slow catch-ups by other players than the US, except it is all out of control, now crippling the US and the Western world itself.

Slap an ESP32CAM on the head of a rocket with a pair of SG90 servos and it'll serve perfectly as a $49 superior substitute to a Stinger guidance block(exaggerating but shouldn't be more than 1.5 digits off). Military technologies and controls on technological proliferation completely missed that, and Stingers are still dumping current on Peltier coolers and spinning those mirror drive systems, genuinely costing thousands to make before bonuses and capped to peacetime rates.

I'm not from the US and I don't identify as an American so maybe I really shouldn't be saying this and I might recall this later in the way some retired American military officials pointing out basic corrective actions to be taken in after the Putin's massive blunder in the Ukrainian invasion - but I think that is the problem that the US military industrial complex is facing, what tech billionaire right wingers were making clumpy half-baked A for effort attempts to fix, and partly why they support what is effectively the destruction of the USA. I think.