Guys have been shooting long range with fixed parallax scopes for a long time, so it IS manageable. But it doesn't come without a burden of practice.
With a "Fixie," draw your face a little out of ideal eye relief so you can see the black perimeter halo. If you hold the black halo even thickness around the rim, such that the crosshairs are centered, then you're not showing parallax. The human eye is supremely effective in detecting concentricity of circles, so a shooter paying attention to it can successfully center the crosshairs and eliminate parallax error in this way even though the crosshairs won't be in focus on the target image. It sacrifices a little size to your eye, and takes a little practice to acclimate - we're all taught the black rim is a bad thing - but it works very well.
