I was pretty young when I learned stealing is a bad thing. I remember a neighborhood child stealing some gum and getting in huge trouble. His mom spanked him (it was the 70s) made him go into the little store with the opened pack of gum, tell the owner what he did, pay for the gum (out of his allowance) and apologize to the owner. He also was grounded for a long time. 
We all had the fear of Mom put into us by this event. Stealing, we learned was a very bad thing that would get us in a lot of trouble. Did I mention it was summer? Kid lost a lot of prime making mud pies and riding Big Wheel time.
I realize that stealing has a different definition for many. For example, a lot of people download music and movies from the Internet illegally. They don’t think it is stealing, or they just don’t care. Politics aside, illegally downloading music and movies without paying for them is stealing under any definition. We can leave the debate aside about how much it costs the industries involved or whether it should be illegal, I have no wish to get drawn into that discussion. But it is currently, and one can assume will always be, illegal.
People often forget that taking something from the Web is also stealing. Copying and pasting an article or picture on a Website is a violation of copyright, so stealing. And taking somebody else’s Slides that a CLE organization has placed on the Web for review or copying them wholesale out of a book, is stealing too.
Some of the best speakers I know are constant victims of having their slides stolen. They are frequently told by colleagues who have attended a presentation done by someone else that the slides they saw at the lecture looked very familiar. A comparison between the original and the new invariably show specific slides or entire presentations taken right from the original speaker’s presentation. It is very frustrating to spend a lot of time creating a presentation only to have someone else take credit for it.
I am more than willing to believe most people have no idea what they are doing is stealing, or are just in a rush and have to have something and don’t have time to ask. And I certainly I understand it is difficult to write a good presentation; but in this case it would be better to not use a powerpoint presentation than to steal one. Not every speech requires slides, and if the speaker doesn’t have time to prepare them, just leave the slides out.
On occasion, I imagine, the sin is worse. That is, the speaker doesn’t know the topic, wants to speak, for whatever reason, and so steals someone else’s slides for their presentation. I get that speaking is a wonderful opportunity to improve the resume or obtain potential referrals. But if someone doesn’t know a topic well s/he really has no business speaking on it.
I have no problem with reviewing someone else’s slides to get ideas. I don’t have a problem with borrowing an occasional slide with proper accreditation. Most speakers are flattered when that happens. Even an entire presentation can be borrowed as long as the person using it checks with the owner first and gives proper credit. But actually taking slides without credit or using an entire presentation without the permission of the creator just isn’t cool.
And no one wants to be uncool, right?