The scroll speed CAN be changed, adjusted, reversed, all of the above - via javascript (or a js library such as jQuery).
WHY would you want to do this? Parallax is just one of the reasons. I have no idea why anyone would argue against doing so -- the same negative arguments can be made against hiding DIVs, sliding elements up/down, etc. Websites are always a combination of technical functionality and UX design -- a good designer can use almost any technical capability to improve UX. That is what makes him/her good.
Toni Almeida of Portugal created a brilliant demo, reproduced below:
HTML:
<div id="myDiv">
Use the mouse wheel (not the scroll bar) to scroll this DIV. You will see that the scroll eventually slows down, and then stops. <span class="boldit">Use the mouse wheel (not the scroll bar) to scroll this DIV. You will see that the scroll eventually slows down, and then stops. </span>
</div>
javascript/jQuery:
function wheel(event) {
var delta = 0;
if (event.wheelDelta) {(delta = event.wheelDelta / 120);}
else if (event.detail) {(delta = -event.detail / 3);}
handle(delta);
if (event.preventDefault) {(event.preventDefault());}
event.returnValue = false;
}
function handle(delta) {
var time = 1000;
var distance = 300;
$('html, body').stop().animate({
scrollTop: $(window).scrollTop() - (distance * delta)
}, time );
}
if (window.addEventListener) {window.addEventListener('DOMMouseScroll', wheel, false);}
window.onmousewheel = document.onmousewheel = wheel;
Source:
How to change default scrollspeed,scrollamount,scrollinertia of a webpage