I'm sure a lot of people agree with you - there has been considerable debate on this topic in other threads on this forum........Al Weyman in particular arguing the same case as you....See this thread:
http://tentenths.com/forum/showthread.php?t=130625
I can see that series organisers need to raise a certain amount of revenue upfront, as they have to commit to circuit hire well in advance, but equally sure that some form of differential entry fees could be sorted, with none-registered racers allowed an entry at a slightly higher entry fee provided no registered competitors are refused an entry - ie whenever there are spare places. Obviously they wouldn't be eligible for points / awards etc.....