Take a look at
SourceGuardian, a very nice program that does obfuscation and encryption on PHP code. It doesn't need any addon's and the code it spits out for the files can be used as is. No server modifications needed.
Now, lets get to the meet of this discussion. Going against OS? Of course, Open Source is about opening the the source of a project to other developers for the purpose of development. Okay, it's not really going against OS, but merely offering another choice.
Does anyone have the right to say "You have to Open Source your product"? No, I don't think so. As much as I enjoy open source products, I don't want to feel obligated to do so. As an author, I would feel very much unhappy if someone used my work on their page without asking, and as such, I want to protect my works as much as possible from that.
The same thing goes with the source code to a program. Now, I believe the problem lies in 2 distinct areas: 1) Who the target audience is, and 2) the nature of the company behind the product.
Unfortunately, most people believe that proprietary products lead to insecure code. This is not true. The development model of open source generally leads to more secure code, but this is not always the case. I have seen just as many proprietary products that are secure as I have see open source products. Unfortunately, the biggest of the proprietary products are usually the most hole ridden code known to man.

I really wanted to say tripe, but hole ridden tripe doesn't sit well.
Anyways, back to the first point - Who the target audience is. It's absurd to think my father could benifit in having PowerPoint open sourced. Now this is where I could throw in the classic "he isn't going to mess with the code scenario" and you would throw back "He doens't have to, but others can, and that means he can upgrade, etc.". I don't use that line because of that reason. However, the fact that PowerPoint is proprietary doesn't mean much to my father. The fact that it works does, and that's it.
Imagine for a second, a proprietary piece of software that works like it should and is the best in the business. Do we abandon it because it's proprietary? No! Look at Photoshop and the open source GIMP. Now, anyone who has used Photoshop (And I am refering to those people who actually know how to use Photoshop, not those that got frustrated with it and went to Paint Shop Pro

) will tell you GIMP is simply not a replacement. Don't get me wrong, GIMP is great, it's very very good. Hell, much better than PSP, and it's free! And Open Source! But what benifits would Photoshop get from opening it's source? It's done an amazing job so far, and in the end, the users of the software simply want to use it. As programmers, we naturally want our source open, so we can muddle around with it and see what is going on.
And that is the crux: Most people who want everything to be open source are not the end users of the products that are open source, and most users who want everything to be open soruce are programmers or developers in some sense.
We like open source products because we feel that we can better trust the company behind the product, but if a company open's the source to it's product, is that any reason to trust them? No, definetly not. A company earns it's trust based on it's actions. If a company does well in supporting it's users, keeping the code secure, and providing necessary patches and fixed when needed, then does it really matter that the source is closed?
One point I will agree to is that companies who stop supporting a product, stop developing a product, or who go out of business, should open source the product. This is not only a smart thing to do, but merely a polite thing to do as well.
Anyways, enough of my hole ridden tripe (whee!), I have probably baited enough of you.
My end point: Enforcing open source is just as bad as what Microsoft does. When you take away my rights to decide what I want to do with my code, that goes against the ideals of a free market. It goes against the ideals of Open Source:
choice.