Why is it difficult to demonize a demon?

I was reading the news stories this morning about the demonstration that was organized by Sadr in support of Hezbollah when one quote from a senior coalition official caught my attention. The story doesn't make it clear whether that official was general Abizaid himself or someone else but I hope it wasn't Abizaid or any official senior enough to influence the strategy of the coalition in Iraq especially at this critical stage:

General John Abizaid, the top US commander for the Middle East, said neighbouring Iran was arming Iraqi death squads, that militias have infiltrated the police and that more US troops are needed to bring Baghdad under control.

A senior coalition official, however, cautioned against treating the Mehdi Army as a monolithic entity, as it is a loosely organized body with only parts actively engaged in violent and illegal activities.
"We have to careful that we don't demonize Jaish al-Mehdi, because look at the polls -- Moqtada Sadr himself is an enormously popular figure. Why? Because he is thumbing his nose at the coalition," he said.
Abizaid, however, also warned against civil war.

(emphasis added)

In my opinion the part about being careful about "demonizing Sadr militias" because Sadr is "enormously popular" is meaningless after we saw (and see everyday) what Sadr is doing and what his intentions are, and in fact this being "careful" can be so harmful to the efforts of the coalition and PM Maliki in dealing with the issue of militias and of course to the hopes of millions of us in Iraq who want to see an end to the violence.

Popularity should be taken into consideration of course, yet it must not be viewed as a deterrent and must not be allowed to be used as one by the militias, and popularity polls even when they show that some leader or group enjoy wide support, they do not mean that we should allow these numbers to intimidate us and stop us from making the decisions or taking the measures that are crucial for the success of Iraq.
Let's look at it from this angle; Saddam enjoyed the same, if not more, popularity than Sadr does today (yes, Saddam was popular among more or less a million Iraqis not to mention popularity among other Arabs) and the same applies to Nesrallah, Ahmedinejad and Bin Laden who have millions of supporters among Arabs and Muslims, however we didn't find it difficult to "demonize" them, right?
I mean should we allow the bad guys to grow more powerful just because they are popular?! This is totally absurd…

According to this "senior official" we are supposed to think twice and be careful before tackling people like Sadr but my question is; if not now then when? Are we supposed to give them more time to grow more powerful and more popular?
We have seen some examples in recent history when crazy tyrants were not dealt with fast enough or powerfully enough whether by an external force or by their own people; putting an end to Saddam would've been easier if the decision was made in 1991 and dealing with Ahmedinejad immediately will be easier than to deal with him when he acquires nukes and disarming the Sadr militias would've been much more easier if the right decision was made two years ago.

After all, popularity polls do not necessarily reflect the truth and today's demonstration indicates that as well; see, instead of the million figure that Sadr was aspiring to see in Baghdad and out of supposedly 2 million Shia residents of Sadr city only 100 000 showed up and that's only after Sadr summoned demonstrators from the southern provinces and sent busses to fetch them and let's not forget that the demonstration took place in Sadr's own stronghold where it's supposed to take no effort from supporters to show up and march; technically they were asked to march in their own front yard.

Let's suppose that the 30 seats that Sadr's followers have in the parliament reflect his popularity, which is not true because they wouldn't have a chance to win 30 seats without joining the UIA and without Sistani backing them, but even then we have most of the remaining powers demanding immediate disbanding of militias. And these are the ones we should consider, not controversial polls of false popularity.

Some Iraqis including their elected prime minister and elected president said 'thank you America' while others said death to America and Iran is strongly supporting those who wish death to America, so what are you in America going to do while we still have the chance, still have the determined leadership and while there's still hope?

Will you stand with those who believe you came to help them, or will you let Iran remain free to push Iraq to doom?