I never understood why in-app purchases have been branded as "evil" in the first place. As long as Apple doesn't offer developers a way to do trials, it's the closest way a customer can get a taste of an app's features, esthetics before deciding whether to pay or not for an app.
EX : I wouldn't have paid 10$ for flighttrack pro without the in app purchase option.
I would go as far as theorize that the main reason why the average price for an app has remained stuck at 1$ is exactly that fear of paying for something worthless without much of a recourse.
It's not In-App purchases, per se that are evil - I've spent around a hundred dollars on new levels (great use of In-App purchase - you reward the developer for creating new content), new tools, new capabilities in the last few years (much less than the the close to a thousand dollars in "up-front" app purchases I've made) - and I think I've gotten real value each time.
What's truly evil, is the cognitive manipulation that "free" games engage in on those who are most vulnerable to those manipulative techniques. The "Candy Crushes" of the world.
You want there to be a virtuous circle, in which developers are rewarded for creating new, and improved apps; not for buying extra boosters so you can clear the jelly without developing the skill required to (or wait long enough for an easier level). How stupid do you feel purchasing "Diesel" for your "Tractor" in a game? Particularly when you consume it and just have to buy more diesel to continue at any reasonable pace.
That's the evil part of In-App purchases - I can show you a dozen places where In-App purchases and/or subscriptions have been very well executed to the benefit of everyone. (LetterPress, Flickr, Whatsapp, Path, evernote, Pioneer Lands, Paper by Fifty-three - just to name a few)
It would be more helpful to show examples where IAP/subscriptions were well executed by your standard and still made it to / stayed in the top grossing list.
ghshephard gave a good answer to the question "why do many people consider in-app purchases evil".
However, there is no doubt that "evil" approaches are more profitable than the doing the right thing.
Techniques such as the ones described in http://www.gamasutra.com/blogs/RaminShokrizade/20130626/1949... are very effective, and developers who do use them are likely to make more money. But that doesn't mean that any means necessary to make it into the top 10 grossing apps list must be considered ethical.
IAP in general is fine, but a lot of these apps are bait-and-switch. They do not make it clear up-front that unlocking critical features requires payment. Games are the worst. There are so many "free" games which simply do not allow you to have fun without spending money. They claim to be free, but then it turns out you have to grind pointlessly unless you pony up the cash. It's gotten to the point where I won't bother with any free app that's listed as having IAPs.
I much prefer the "Lite" model, where you basically have a functional demo for free, then a separate paid app. Offer the paid features in the "Lite" version as an IAP too, if you think that helps.
What it comes down to is that a good transaction should be a net gain for both sides. I give you money, and in exchange I get something that's worth more to me than the money I give you. We both win! But the way many of these games are done, the creator deliberately makes their game less fun in order to make it more lucrative. It's no longer mutually beneficial. Rather than adding value to get more money from me, they actually reduce value to try to extract more cash.
Seems like an argument for a sensible trial system, not IAP. I've got no problem with using IAP for a sensible trial system, but it is much more commonly used for smurfberries.
EX : I wouldn't have paid 10$ for flighttrack pro without the in app purchase option. I would go as far as theorize that the main reason why the average price for an app has remained stuck at 1$ is exactly that fear of paying for something worthless without much of a recourse.
in-app purchases all the way.