LEO has enough atmospheric drag to take care of most of it. At higher orbits it might be a problem, but humans mostly want satellites that help earth activities, which usually means LEO is preferable. This is actively monitored and worked on.
Not being able to leave the planet is not really ever going to be an issue.
Space debris can make specific orbits unusable, but you can pass through those orbits no worries.
You can think of it like the asteroid belt.
If you are flying out past the asteroid belt you don't really need to worry about it, as the objects are spread out so much your chance of intercepting one is very small.
If you want to have an orbit within the asteroid belt you will definitely need active course correction and obstacle avoidance.
Of course, there is a point in which if there were truly stupid amounts of debris in a specific orbit then you might have difficulty avoiding it, but that seems incredibly unlikely - if only that we would stop throwing debris into that orbit way before we got to that point.
> One implication is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges difficult for many generations.
[Edit]
And farther down under 'Implications':
> the resulting debris cascade could make prospects for long-term viability of satellites in particular low Earth orbits extremely low. However, even a catastrophic Kessler scenario at LEO would pose minimal risk for launches continuing past LEO, or satellites travelling at medium Earth orbit (MEO) or geosynchronous orbit (GEO). The catastrophic scenarios predict an increase in the number of collisions per year, as opposed to a physically impassable barrier to space exploration that occurs in higher orbits.
Newer satellites usually have a fuel budget to de-orbit or at least go into a parking orbit.
That, plus there's work on de-orbiting passive objects from earth or from cleaning satellites.
I'm with GP that this has huge potential, even if it's not in the hubble class.
Right now, it's not a big deal if 1% of satellites die before they can deorbit or go to a graveyard orbit. When there's thousands of satellites going up every year I think it starts to become a potential issue.
https://en.wikipedia.org/wiki/Kessler_syndrome