That is what every indicator is... an indicator manipulates the fundamental datasets (price and volume) to produce another dataset...

Why spend all your time on trying to read another dataset when you've got the original and most reliable right there in front of you?

What if you had positive expectancy without these indicators? If anything you'd have less to worry about if all you had was price and volume and thats it.

Alot of people claim to trade without indicators on this forum but then they through in a couple moving averages here and there... Moving averages are still indicators!

Why spend all your time on trying to read another dataset when you've got the original and most reliable right there in front of you?

There are two types of indicators: those which you personally choose that help you to view the market optimally and/or make your own personal trading decisions, and those that are "common" to a large group of traders and are essentially self-fulfilling prophecies.

The first types of indicators are optional, because nobody else is really reacting to them, and so it's just your personal preference whether you like to use them or not. The second type, however, are important for everybody to be looking at, even if you don't use them in your personal trading decisions.

For example, anyone who is daytrading without having at least the following 2 EMAs on their charts is at somewhat of a disadvantage:

20 period EMA on the 5 minute
20 period EMA on the 15 minute

You don't have to have a 5 minute chart or a 15 minute chart open, but if you don't have these lines drawn on whatever time frame you are looking at, it's like not being aware of important resistance and support levels that 80% of the rest of the market is using. Sure, you can always detect that a trend is slowing down at these levels using price action or other measures, but knowing where these lines are ahead of time and how other traders will typically react to them is a big advantage.

Now personally, if I was designing a trading system from scratch, I probably wouldn't have chosen these particular periods as being very important, as I think that there are probably better ways to view the market... but my personal opinion in this case is irrelevant, because so many other traders look at these things. Since tons of traders follow these averages and place their orders around them, if you don't have them on your charts you are missing some valuable information about support/resistance areas in the market.

There are other well-known MAs on different time frames that are also used by a number of traders, which become self-fulfilling prophecies as resistance/support areas as well.

So I would say that while many indicators are not really necessary, the more common ones like the two I mentioned are very useful for "spying" on what other traders are looking at and taking advantage of them.

I've spent 8 years trading professionally in London and Zurich. I've never met another professional trader trading any decent size that relies on indicators that has actually made a career out of trading. The markets are dynamic, indicators are not. Indicators are set to a mathmatical formula, which is pretty useless for intraday trading. Remember that essentially the market is just people buying and selling and the shift in supply in demand is what moves price. If you want to last in trading, and trade more than 10lots (futures) in your trading career, you're going to have to learn how to read order flow so you can actually see for yourself who is in control of the market. The opportunity to trade lays where there is a shift in supply and demand. By the time indicators give you so called 'signals', the opportunity has been and gone, which tends to lead to you getting involved in the move late, leaving yourself open to being squeezed out.... sounds familiar?

Learn how to read orderflow and open interest

Remember that essentially the market is just people buying and selling and the shift in supply in demand is what moves price.
If you want to last in trading, and trade more than 10lots (futures) in your trading career, you're going to have to learn how to read order flow so you can actually see for yourself who is in control of the market.
The opportunity to trade lays where there is a shift in supply and demand. By the time indicators give you so called 'signals', the opportunity has been and gone, which tends to lead to you getting involved in the move late, leaving yourself open to being squeezed out.... sounds familiar?

Learn how to read orderflow and open interest

I think that this statement goes directly to the heart of the matter, but the problem here is that some people are using different definitions for the same set of words.

When some people say "I think that you can/should trade with indicators", what they are saying is that you should use indicators for your buy/sell signals. Meaning, when one line crosses another line or some such thing, then you enter/exit your position. It is this type of "indicator trading" that people like Lynx21 (and myself) would say is not very useful, especially in intraday trading. As he points out, things move too fast for that type of trading to be very successful, and order flow/price action is what it's really all about.

However:

That doesn't mean that indicators are useless. This is where we get into the second definition of "trading with indicators", which is how I do it. I use a couple of moving averages and bollinger bands to help me to frame the price action / order flow that I am seeing. 9 times out of 10 I will see/feel price turning before an indicator has given an official signal, just by watching the price action itself along with market structure.... but this doesn't mean that the indicator itself is of no use. If used correctly, it can give you a framework in which to interpret the price action, and that can help in certain situations, especially when markets are moving very quickly.

For example, if you have a long and a short moving average, their relative angles and positioning can tell you a lot about where the market currently is, and so when you start to see a certain type of price action occurring, those moving averages can help you to interpret it in context. Do you need them? No. Do they help in any way in generating trade signals? No. But they can help in giving you a kind of "visual shorthand", that at a glance, can tell you what type of state/position the market is in. It is especially useful on a visual level if you have multiple time frame charts up with the same moving average plotted on all of them, as this can visually help to "sync" things up between the charts. Of course, some people find this type of thing confusing because they find that it interferes with their ability to read price action, so if you are one of those people then you should definitely just clear your chart completely and look at only price, because that is by far the most important thing.

Each person has individual preferences for what looks and works best for them. So if you want to use indicators to help you to "frame" price action, then go ahead. But as Lynx21 says, if you use them for your trading signals and try to trade mechanically in some manner, especially intraday, you are going to be in trouble. Even if you somehow could make money this way, you would never be anywhere near as good as if you learned how to read order flow and learned to detect changes in supply and demand.