Earplugs don't affect your rhythm.

Not rhythm but everything else involved with playing an instrument within an orchestra, from different levels of loudness to softness to the exact pitch of an instrument.

Classical music has a great deal more variation in terms of what level of loudness a piece should be played at and a piece can drop from a very loud portion to a very soft level within one note.  There might not be time to take out earplugs between the loud portion to the soft portion.

Also, instruments for symphonies depend on the musician being able to hit each note in tune.  It is definitely possible to be perfectly in tune for one note and be jarringly out of tune on the next note, whether it be a woodwind, string or brass instrument.  A very slight change of the lips or a finger position can make a big difference and catching a tuning error quickly means the musician must be very attentive to the exact way his instrument sounds.  

Do you have much experience wearing earplugs?  I wear them quite a bit at work, and sometimes don't even bother to take them out at lunchtime.  They don't interfere with conversation, except that your own voice sounds a little bit louder in comparison to others.  They definitely don't affect your sense of pitch.

The basic effect is to mute sounds roughly in proportion to how loud they are.  You might not be able to hear a soft whisper, but otherwise you hear what you would otherwise hear.  In a loud environment, you hear more, because the masking effect of the loud sounds is reduced.

Given the importance of hearing to a musician, I think it's foolish not to wear earplugs when you are exposed to sounds above about 100 db, whether they are musical or not.  There are hi-fi earplugs available that give only 12db of attenuation.  That's enough to bring a potentially damaging volume down to one that is pleasantly loud.

I've suffered quite a bit of hearing damage, and so I tend to be a lot more careful about my ears than many people.  You can live and learn, or you can listen and learn.

"Do you have much experience wearing earplugs? "

Quite a lot, myself.  When you're a target shooter with half a brain, you learn to use them all the time.  

I've tried both passive and active earplugs, but the were rather uncomfortable.  Then I went with passive earmuffs.  Those were OK.  Now, I'm using electronic earmuffs.  You can hear fine (or even better than normal) at lower levels, but they clamp down at 85db, as much as 27db.  They do require AA batteries, but they last ~200hrs, and I've got at least a dozen (maybe 2) rechargeable NiMH batteries here.  Twenty bucks -- cheap insurance.

there's only one way to find out...

I understand that the intent of this law is good.  However, music is actually a very physical activity and it is not uncommon for musicians to damage certain portions of their body during a long career.

When I was in college, one of my friends ended up damaging the ligaments in his hands.  His intent had been to try and become a concert pianist.  In the end, he had to settle for playing the harpsichord which does the stretch the fingers as much.  I also used to have my right hand in an ace bandage for several years because the weight of my instrument was resting on the thumb of my right hand.  It wasn't too bad when playing for a brief period, but after two hour practise sessions, my whole right hand to midway up the lower arm would be burning.

I don't play any more because I just don't have the time to practise daily (it's amazing how quickly such skills can just disappear if not done daily) but for those who do become musicians by profession, they are aware of what they are putting their bodies through, whether it be the risk of deafness or tearing up certain muscles and ligaments.

I'm in the same boat.  I injured the nerve through my elbow (cubital tunnel syndrome) playing ukulele, because you cock your elbow more than is safe when playing.  Now, I can play guitar as long as I like, but when I stop, it feels like someone has been beating on my forearm with a baseball bat, and it lasts for weeks.  THe worst thing about it was that I felt like I was finally starting to "get" the guitar.

I shifted to slide guitar.  I like it, but I can't play as casually because there's quite a bit of setup involved, and I always end up in a fight with my girlfriend over volume levels, even from a tiny 9-volt amp.  God help me if I try to play through my 15-watt amp when she's in the apartment.

Then she says,"No, I love it when you play."