The way I look at it:
Take away the World Cup spot for Africa, you take away everything they build up and play for. There is nothing for them to play for (don't tell me repechage, cmon man).
Why not repechage? There would be 2 repechage spots if you took away Africa 1, giving African teams ample opportunity to qualify.
South American teams have a chance to qualify straight through, they play the US/Canada loser.
That is in no way qualifying straight through. It's effectively a modified repechage spot between North America and South America. They have little chance in those matches and it is still not an automatic spot. And by that logic, why not have the US/Canada loser play Africa's champion? After all, they'd still have a chance to qualify straight through according to you. See how silly that sounds?
Every team has a legit shot for an automatic spot (meaning to repechage playoff). What reason are people going to have to develop and play high level rugby in Africa if there is no chance for a one in a lifetime chance at a World Cup?
There would still be a chance via repechage. If you aren't good enough to beat the likes of Uruguay, Chile and other teams at that level, you really shouldn't be at the RWC. And no, not every team has a legit shot at an automatic spot. South America does not in any way, shape or form.
I understand that Africa is a weak rugby continent, there were times when others weren't so great either. Based on your logic, I get the sense that you would've taken away Asia's spot after 1995 because they got blasted 145-17 by New Zealand, and that wasway worse than any result in the previous World Cup.
I would not have taken away Asia's spot for 2 reasons:
1) The continent of Asia would have had no representative in the RWC. Africa would still be represented by South Africa in this case.
2) Japan had actually won a match in a previous RWC. Naturally, the team they beat was the African qualifier Zimbabwe, by 44 points.
The IRB needs to develop African rugby. Giving them a 2nd spot in the RWC so that the world can watch them get crushed by everyone from Fiji to Georgia doesn't accomplish that. What will develop African rugby is grassroots development and placing players in professional training environments.
And again, I am not in favor of giving South America a 2nd spot in addition to Argentina, but you can't apply the arguments you apply to Africa without doing the same to South America.