Yes you can.
Question for you now, why would you think playing a Blu-Ray would 'mess your system up'?
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This crap is surfacing again?? I swear...
Now, let's be logical. How is playing Blu-Ray movies on the PS4 going to damage the system when the games themselves are on Blu-ray??
So you go and buy a lot of games and a lot of movies!!!!
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The PS3 is the reason the Blu Ray medium beat out HD Disk. Of course the PS4 will play them and no it will not damage the player. I game is more likely to cause you PS4 to over heat or the moving parts to fail than watching movies.