I have always found this fascinating. We are the most intelligent beings on the earth. Still, a rat can give birth to its offspring all by itself, but why is that not happening with humans? Is it just for psychological reasons? Or have humans become weak? If there is a young girl who doesn't know anything about giving birth, what are the chances that the baby and the mom will make it?
One of the core reasons for this is actually a side-effect of the 'most intelligent beings on the planet' - we have very big brains.
Evolution has taken us pretty much to the limit on size at birth - we are already almost the least developed physically at birth. Many mammals can walk an hour after birth, but we have developed large brains, and large heads.
A certain amount of adjustment to a mother's hips has also taken place - widening more would severely impact the ability to walk or run.
What this means is that there is a small, but real risk that the baby will not be born unassisted, and that there is a fair amount of stretching and relaxing required during birth, as well as the potential for stitches and other medical assistance afterwards.
So many people prefer to have this assistance with them, just in case. Especially for their first child.
Humans are fully capable of having unassisted births, and many chose to have them. Tradition, herd mentality, increased medical knowledge, and (unfortunatly) economical gain have shaped the way child birth is carried out in the world today (with great variety), but the way we birth says nothing about our physical capabilites to do so on our own.
It is entirely impossible to say how any birth will end, complications can arise in a hospital birth, or unassisted or with a midwife at home. In both cases complications may arise from malpractice or unforseen events. A birth that could have ended well at home unassisted could go terribly wrong in the hospital (due to a high level of intervention, for example), and vice versa.
I would like to add (to expand upon @Adam Davis' comment) the concept of infant mortality.
Because of our civilisation and technology we know that by even some basic intervention the risk of mother or child dying in child birth can be reduced.
In the last century or so we have reduced mother's death in childbirth from 1% (my great-grandmother died in childbirth for example) to 0.013% (I personally know of no one in the modern era dying in childbirth) and infant mortality has fallen dramatically (depending where you're born).
We simply don't think this way about non-human animals reproduction.
According to some seconds of internet research: about 1% of cats and 2% of dogs will have birthing related complications. Apparently this number in unassisted cattle and goats births is very high. Apparently miniature horses nearly always need assistance, as do many small breeds of dogs, for example some breed of Chihuahuas can need cesearian sections.
So really in a reproductive sense we're normal animals, but yes, with very big brains that in this regard we've used in a good way (to save more women and babies!).
There's the whole other discussion about "litter sizes", which is the work around in case some % of your offspring just don't make it. Obviously many animals use this strategy. But that is a different Q&A.
There's a big difference between "need assistance" and "want assistance" in childbirth. Think about what our culture communicates about childbirth. Many describe it as 10 times worse than a visit to the dentist.
No surprise that so many want assistance. And since it will only happen a small number of times for most, arranging for assistance is no big deal. Most deliveries are about pain management. That is not to say there aren't real needs in birth. But statistically, they are small numbers.