Everything was just more conservative during the times of Phantom of the Opera. The way people dressed, the music, everything was rather subdued in comparison to recent years. As the country let go of its inhibitions, everything became more blunt and graphic. 

Much can be said for the way the director builds suspense in these films.  Certainly the added bonus of amazing special effects can increase the realism, but there are films that have been put out recently that I found incredibly suspenseful and frightening (Like Super 8 by J.J. Abrams or Signs by M. Night Shyamalan) that did not rely on super violent scenes to make the movie scary.  Sometimes the power of suggestion and the audience's own imagination are the best combination for making a scene truly terrifying.

I tend to agree that it is the special effects which have made film more frightening. For example, showing a person unfamiliar with horror movies Phantom may not scare them as much as Nightmare. That said, even more current horror movies push the envelope, because it takes a lot more to frighten audiences today.

I would suggest that if Phantom was remade, using the special effects of today, it would be far more frightening than past adaptations.

There is also a greatly different availability of "special effects" techniques that can be, and seemingly are whenever possible, used to heighten the effect of the violence. Because this has happened so often in so many situations, society does seem to be more accepting of such violence - which leads producers to push harder to find ways of escalating the violence even more.

I would suggest that it seems our current culture is more inundated with violent media, specifically movies, television, and video games than was available 60 years ago. The more exposure there is, the more commonplace or acceptable it becomes. The one thing that you can say about all violence in media is that the audience derives some of the pleasure from the fact that it isn't actually happening, especially to them. 

First, I think the point should be made that we can reasonably compare the depiction of violence in these films, yes, but we can't reasonably compare the cultures which produced the films based only on these two isolated examples.  

There are now (and always have been) varying degrees of gore in film. There are different kinds of violence depicted within every era of film. It's true that from generation to generation the norms shift, but we can hardly say that there was once one way to depict violence and now there is another way. There have always been various temperments on display in film and thus various treatments of violence.

Though graphic violence is certainly more commonplace on screen today than it once was, there are still many, many films that deal with violent subjects yet refrain from gore, blood, and guts, focusing instead on suspense and emotional or narrative content. For this reason we would be amiss to claim that film has categorically become more graphically violent. 

If the question we are addressing here is "Why is graphic violence more commonplace today than it once was?" then we can also ask "Who is behind this change, the audience or the filmmakers?" 

I think that it just shows that people in our society are restless and that they like to "push the envelope."  People are not content to have the same old stuff.  They want things to "progress."  We can see this in the violence, but also in things like sexual content and language in films and on TV.  There is a constant desire to be more and more "out there."  I attribute it to a desire for novelty that seems to pervade our society.