I don't think you thought this one through... if anything you're making the opposite point you're (I believe) trying to make.
I'm writing this on a macbook air that sizes up to <2.5% of the weight and volume of a desktop computer you're describing (screen, case and peripherals). It's also idling at about 2-3 watt, which is also <10% of the computer you're describing. It also produces much less sound, it's entirely quiet.
So size, weight and power usage and noise are way down.
The idea that I'd use a pentium 3 instead is ridiculous for these very reasons (heavier, bigger, noisier, using more energy), even in private use, and especially in public use.
It's also the reason why bigger, heavier, noisier and more energy-consuming cars, are also ridiculous to many people, particularly those not driving them and having to face them in the public sphere.
Why is it wrong to have a powerful vehicle if you don't always use it for tasks demanding that power, but it's okay to have a surplus of power for low-demanding computing tasks?
Same reason I don't want to have dinner in a restaurant next to someone trying to cut their steak with a chainsaw: at best they are being incredibly obnoxious, at worst they are going to maim me. Just because it is better for your once-a-month weekend lumberjack trip with the boys doesn't mean it is an appropriate one-size-fits-all cutting tool for day-to-day use.
Contrast that with someone having a needlessly powerful computer. How does that impact the rest of the world? Not at all, it only impacts the owner's wallet. Someone's needlessly-powerful computer has never killed a child, or taken up four spots in public. Heck, it'll even downclock when idle, so there isn't even any extra power use to be worried about!
Because accomplishing the same task with a more powerful (i.e. larger) vehicle is a) more polluting, and b) more dangerous for other road users; two things that are not true for a surplus of computing power.
Nope, it's not! It's more than the bare minimum I need, and also larger than an appropriate moderate size (let's not shift the goalposts here) because - unlike a vehicle - operating a larger-than-appropriate home is _barely_ more polluting, and no less dangerous, so my indulgence has negligible negative externalities.
Thanks for playing! Wanna try again?
---
For anyone else reading this, the issue that monkeyelite's comment had was the false equation of "it is good to prosocially take others' safety and comfort into account when making choices about personal behaviour and consumption" with "one can never use or consume any more than the bare minimum". This is a classic approach that the American right uses when criticizing any prosocial policy - the immature that the only choices are selfish indulgence and bare austerity. It's possible to be comfortable and even lavish while being a considerate member of society. Using/consuming/polluting less is always good _in isolation_, but can and should be measured against the benefit that it accrues to you _and_ the externalities imposed on society.
The obvious counter-argument there is "I don't care about other people, I want my big truck, and I don't care (or, I actively like) that it endangers other people". Which, well - if that's your viewpoint, you're welcome to hold it, and others are welcome to judge you for it.
Because by and large the apps and programs you are running on your computer requires lots of resources just to open and allow you to do your low-demanding tasks.
I'm writing this on a macbook air that sizes up to <2.5% of the weight and volume of a desktop computer you're describing (screen, case and peripherals). It's also idling at about 2-3 watt, which is also <10% of the computer you're describing. It also produces much less sound, it's entirely quiet.
So size, weight and power usage and noise are way down.
The idea that I'd use a pentium 3 instead is ridiculous for these very reasons (heavier, bigger, noisier, using more energy), even in private use, and especially in public use.
It's also the reason why bigger, heavier, noisier and more energy-consuming cars, are also ridiculous to many people, particularly those not driving them and having to face them in the public sphere.