It may be a naive view but, in some areas at least, one can choose to spend one's trading profits in a way which benefits society, e.g allocate a portion to charitable donations, buy environmentally/socially sound products like organic food from local suppliers , while avoiding consumption that clearly does not, e.g by spurning McDonalds or enormous gas guzzling MPVs (just a couple of cliched examples). Spread bettors especially can avoid personal income tax and hence their profits are not subject to the whims of government public spending, e.g on moral grey areas such as defence. We have a lot more choice in where our money goes than perhaps a more conventional worker does, although I appreciate that the spread betting companies pay betting tax "on our behalf" as it were.
The simple act of consumption, if done carefully, can benefit society IMHO.
I also like the fact that trading is a "clean" business. Apart from a smidgen of pollution caused by PC electricity consumption there are no unsavoury by-products from trading that I know of, which is certainly not true of many commercial businesses that one could work for.
Production is defined by Ayn Rand as "the application of reason to the problem of survival" which (if you agree) would suggest that to be a productive member of society one does not necessarily need to make tangible items or provide direct services to others.
And, as Glenn says, if our conscience piques, we can choose to spend our free time addressing issues that concern us.
