As mentioned by others, this is no different than selling naked straddles; the underlying positions are just superfluous expenses. Selling straddles is generally considered a long term profitable strategy, but with the potential for terrible draw-downs so that money management requires only taking tiny positions. It's probably wiser to hedge your short straddles with long strangles (Iron butterflies) so that you can know your total risk per spread, giving you a better handle on how much money is prudent to spend on a single trade. I've head that it's best to use 40 - 80 days until expiration and to sell winners when they reach 25% of maximum potential profit.
I am in agreement with markuzick. You can profit from short straddles in the long term, but you must do certain things:
1. Be prepared for terrible months (including stretches of several terrible months in a row), therefore...
2. Trade small, and buy some wings--so now you have butterflies as markuzick has wisely suggested. The wings don't have to be very close to the short strikes. As long as you have some kind of wings you can avoid getting crucified if you manage your money correctly. No matter what you do, you will still have trades with 100% losses. So, a small fraction of your money is best for this. Options are like alcohol: a little might be good for you; more is not better.
3. Have a strategy (set of indicators) for exiting all trades when the market is bad. Even though butterflies are supposedly neutral, they should still be considered a fair-weather strategy. You don't want to be messing with these in a time like 2008. For example, here are two simple rules that could be used as filters/indicators for getting flat: UL below its 4-wk MA OR VIX >25. You don't have to use these rules exactly, but you should use some sort of rules, and you should backtest them.
4. Choose an underlying with liquid options.
5. There are a lot of ways to manage these (see David Caplan, Larry McMillan; not sure whether the people on Tasty Trade can be believed since they clearly want to get people to trade more). But, you don't have to manage them, and it might be better not to. I'm not sure whether any method of management is necessarily superior.