The author does explain why financial activity is desirable. It is important for business to be able to diminish their risks by trading in options and futures.
You should also not state an assumption that 1% of financial transactions are involved in financing real activities, then ask "Disprove if you can". If you have an opinion, it is your business to defend it. Otherwise you just invite answers of the type: "I believe you have no idea what you are talking about. Disprove if you can".
There is no reason to believe that a transaction that is extremely low profit is unrelated to the financing of real activities. A small business is in constant need of small sums to be repaid next week. Whenever you order something, the business you buy it from has to build it first, give it to you, then ask for your money. Where do you think they get the money for the materials? They make a small loan, for a couple of weeks. Of course, the transactions are low-profit, because the bank does not charge much interest for such a small period. One of the largest impact of the recent crisis on small businesses is that they were unable to secure these small loans from banks, because banks were too scared to lend.