The issue is that if there is a flood of transactions, like an attack, it will impact the network. Hopefully the devs can implement fixes which can allow us to hit 1 million TX per day with no issues.
If attackers know that they can cripple the network with a particular attack then we are in a bad position. It would be very expensive to flood that many transaction on mainnet, but it is possible for someone with deep pockets.
The issue is that if there is a flood of transactions, like an attack, it will impact the network. Hopefully the devs can implement fixes which can allow us to hit 1 million TX per day with no issues.
If attackers know that they can cripple the network with a particular attack then we are in a bad position. It would be very expensive to flood that many transaction on mainnet, but it is possible for someone with deep pockets.