i think this comes down to planning your hike ahead of time...if you know your not going to be able to do the amount of miles needed to make it to the next camping area maybe you should not do the hike.....
hike on another trail that will let you camp where ever you like
it's different if your hurt or something went wrong and you need to stop for the night ... but to plan on camping illegally ahead of time is wrong
camping illegally without knowing is one thing
camping illegally and knowing you are is another thing .... stuff like that is what gives hikers a bad name if you ask me
don't forget it's stuff like this that will give reason to close down a trail or a park .... and don't have too many left