>>abraco+nt1
The usual way of solving this is to make the voucher responsible as well if any bad actor is banned. That adds a layer of stake in the game.
>>speps+Qv1
A practical example of this can be seen in lobsters invite system, where if too many of the invitee accounts post spam, the inviter is also banned.
>>supriy+mA1
I think this is the inevitable reality for future FOSS. Github will be degraded, but any real development will be moved behind closed doors and invite only walls.