I was one of those that preferred slideout-keyboard phones for the longest time. However, earlier this year, when I was considering moving to a phone without one, I tried an experiment. For 2 months, I went without using the hardware keyboard, using the touchscreen exclusively. Surprisingly enough, it turned out that the software keyboard was faster and more efficient, most notably due to the swipe capabiities. For the most part, I found I could live with it, minus some inconveniences. First, it does use up screenspace when you're typing, but I find that when I'm typing I don't really need much screenspace anyway. Secondly, entering in non-standard text, such as console commands when I'm using ssh, is slower and less reliable. But those cases turn out to be few and far between. (The ssh sessions tend to be short, and if they need to be longer, I'm more likely to pull out my netbook for the task anyway. Yeah, I still use a netbook. 5 years old, and still a beast. But that's for another thread.) And finally, the tactile feel of pressing the keys, along with the individual key precision is really nice to have.
But despite that I've been using a touchscreen-only phone for about half a year, and I don't really mind at all. Neither the slideout nor the touchscreen is ideal, but of the two, the touchscreen (on modern phones) probably has enough benefits to give it the edge.
Some other things to consider: Slideouts are more prone to breakage and malfunctioning. They add to not only the monetary cost, but also the time cost of the phone. They make the phone bulkier and less marketable. They make accessory design more complicated.
And here's a really important one to consider: Language. With a software keyboard, there is virtually no effort required to make a phone accessible to any audience, in any country. A keyboard requires a lot of extra manufacturing considerations and iterations to deliver the same accessibility.
On the downside, it's harder to get a software keyboard to work out for the vision-impaired, but for the most part, hardware keyboards are hardly ideal in that area too.