A 51% attack is unlikely, but if there is less incentive to mine the that could change. Since the burden of incentivizing is going to be increased transfer fees, the already high bitcoin transaction fees will become too high. At some point in time (I'm not sure when since I don't know if doubling the transaction rate will double transaction fees) people will look for a cryptocurrency with lower transaction fees. I think that will be Bitcoin Cash. Litecoin does not limit as much inflation, but that would be my second choice. It can process transactions faster. If reaching consensus proves too difficult for bitcoin to evolve Litecoin could prevail over Bitcoin Cash.

That assessment is based on the transaction fee you told me though. You said it was about $15. Is that for all transactions or is that relative to the amount of the transaction? If it is the latter I might reassess that. If it is the former it is not practical for small transactions. Isn't that a problem?

If the shareholders of the Federal Reserve System (known for hating competition and waging war costing trillions  to protect the petrodollar) decided to invest billions or even trillions to do a 51% attack to sabotage bitcoin and were successful, what is the worst that could happen?