Mostly I don't have any problems with backmarkers, but there are some people who can't seem to think. For example, if get behind someone on Aston National, on the last hairpin, the backmarkers usually wait untill the straight before they pass me. I can't stand that. In 9 of 10 cases the backmarkers does something stupid in the chicane, for example crashing in the tyres. Just because he's under pressure. So please, let people pass before the chicane..
And of course when you join in mid race you should go off the line and brake if needed, for the race leaders. You got absolutely no rights when you join midrace, imo.