When you consider the vast number of galaxy's and planets there has to be other intelligent life out there.
OK, I'll play devil's advocate: why does there "have to be"?
Let's start with one simple fact: we have only one data point for any of this. This means that we have no alternative but to consider Earth as "typical" in terms of the probabilities, speeds of development, conditions needed, but if there is in reality only one place in the universe where life started
nothing we know about how life starts or develops would look any different from how it does to us now. If you have a single measurement you have to assume that represents the true value (within experimental errors) but you cannot know that you weren't unlucky and didn't get a highly atypical value. Extrapolation from a single data point is very risky.
So what do we know?
We don't know how life starts, and we don't know what conditions are needed. You hear people talking about theories (often different ones), but we don't actually know. Therefore we don't know how easy that process is, or how common the conditions are. The one thing we know that's favourable is that it happened rather quickly on Earth, but if in fact it's very difficult and we just happened to be lucky here we would not be able to tell.
Then there's the development of complex life. This would appear to be difficult: for 6/7 or so of the history of life there were no multicellular organisms. Maybe we were unlucky that it took so long? Or maybe we were lucky that it happened so quickly? We don't know. But planetary conditions can change a lot in a few billion years, so if something takes a long time there's a risk that it may not get the time it needs.
Related to that: how likely is it that a planet can maintain liveable conditions for long enough? If it's too small it will lose volatiles (Mars). If it lacks a strong magnetic field it is similarly vulnerable. If it is large enough but lacks plate tectonics it's vulnerable to accumulation of greenhouse gases (Venus). These are a couple of things we can see from our single solar system, but there may be other vulnerabilities that we've not considered because we don't have a nearby example. We do know that the Earth's magnetic field relative to its size is anomalously large, possibly related to the event that gave it an unusually large satellite (which also helps stabilise its axis, again producing longer-term stability of conditions for any life trying to evolve there). If intelligence takes time then we can probably rule out dense clusters of stars, places where the orbits of planets or debris belts/clouds are likely to be disturbed on timescales of tens or hundreds of millions of years.
And of course we have no idea whether evolution of anything like the sort of intelligence that we mean when we talk of "intelligent life" is likely or absurdly unlikely, nor how long it's likely to take. However while this might appear simpler than the leap to multicellular life (based on our single data point) I will note that it's almost certainly more vulnerable to disruption. And as Arthur Clarke noted, the survival value of such intelligence is not yet proven: we're certainly doing our best to collapse our civilisation and ecosystem within the first few millenia of recorded history.
I'm only scratching the surface here, but this post is already too long and so I'll stop now. My point is that there are huge uncertainties in any aspect of this question, and so I would never accept any statement that there "has to be" anything (again, whether that statement is positive or negative). The one thing I am sure of is that if we could turn the clock back 4.5 billion years and run everything again there would not be a bunch of bipedal apes discussing it at this point (but whether that would mean that some entirely different organism would be busy colonising the galaxy or the Earth would be a snowball inhabited by nothing more complex than cyanobacteria, I would not like to take a bet on).