It's really quite simple, and doesn't require an extensive blog post.
The motivation behind DRM is 'preventing piracy'. Seeing as virtually every method of DRM is cracked straight away (let's not forget that software crackers see this as a fun challenge), that motivation is somewhat invalidated.
On the other hand, DRM presents problems for paying users, to the point of publicly shaming someone that legitimately purchased the software, or even permanently destroying many hours of work by legitimate users.
- DRM does not have the positive effect people want it to have
- DRM does have many negative effects
Conclusion: DRM is bad.
If you so much as think about responding to this with "but we have to fight piracy!", then you should pause now, and think to yourself whether stopping piracy is really your motivation, or whether you're just looking for a way to feel good about "inconveniencing those nasty pirates". After all, we've already seen that DRM does not contribute to "stopping piracy".