I find that when racing on-road (not oval) trying to stay on the lead lap is not necessary. With lap times usually in the 9 to 15 second range, you are not going to get back up and catch the leader in most cases. If you REALLY think you have a chance of catching the leader later in the race, keep racing, but be truthful with yourself.
I find that when I am following some drivers I am not able to keep my car 1 or 2 car lengths back and not hit them. In some cases my distance varies between sniffing the exhaust and 10 car lengths during a lap. Different driving lines and leaving room for the car in front to not take me out if they make a mistake can make following closely difficult.
Basically, if it is not for position and the driver behind me has caught me and makes one attempt at a pass I then assume I am holding him up and will make room at the first safe place. There are places on some tracks where I will NEVER let someone pass. Just let them know you are going to let them go and they will be patient with you.
It all comes down to being respectful of each other. You respect the fast guys now and you will get the same respect when you are the fast guy.