I actually like this feature for going to the movie theatre and work. I love movies and don't want to be bothered while watching them and am also annoyed when people are on their phones while I'm trying to watch a movie I paid good money to see. At work, I DO periodically check my phone in case someone tried to contact me in an emergency.
If you don't want to use the buttons on the side, there are widgets that will throw your phone into vibrate mode with just a screen press. Also, if you're interested at all in home replacement apps, the status tray on Home++ is REALLY handy for this. Clicking the speaker icon toggles the phone between ring, vibrate, silent, and back again.
Just my opinion and some options, though I can understand why you'd rather just have the ability right on the lockscreen!