I meant that the core team is harvesting with their own coins, not with funds.
It's catch 22. If you don't harvest with these funds then you lower the security of the blockchain, if you do harvest with them then you make NEM a non-decentralized system. The only solution is to split harvesting among several people who will likely not collude.
This isn't really an issue. The funds held in for the Sustainability Fund are meant to be distributed quickly for the most part, within 1 year or so. Security is also not an issue at the moment, as currently all nodes seem to be good actors.