How can the cost of transactions become arbitarily high? Mining is a competitive enterprise right now. There is a option in the client to select a maximum processing fee, doesnt this communicate to transaction processors how much they can make by securing your transaction? If clients pay less than it costs to secure the transaction, the transaction is not processed. But if the processor is too greedy and doesn't accept low fees, he will be driven out of the processing market by a processor who is willing to accept the lower fee. The key is that the software is open and free, so the market for processing is huge, and there will always be competition.
Bitcoin has many tangible benefits for its users in comparision to regular finance: anonymity, security, universal acceptance (eventually). The value transfered to processors is well worth the benefits to the client, or clients would not use the system. Some value MUST be transfered to processors, because processing takes energy to undertake, and energy is not free in any sense.
The a question posed is "how many miners do we want?", the answer is we don't want ANY "pro miners".
Currently there are people heavily invested in mining: "pro miners". This group is an anomaly, almost a cancer that has grown on the system. Will these "pro miners" shut down and dissapear once their business becomes anything less than lucrative? For sure. Will bitcoin transactions slow to a crawl? Eventually they will. Will the curency devaluate relative to dollars? Eventually it will. But the currency will always have non-zero value due to its scarcity and it is and always will be traded for other goods/currencies. We can sit back and watch the variance while the system takes time to mature and become a well distributed system where the only miners and payment processors are the users themselves.