Quote Mike Stranks:
... if you need earplugs it's too loud - end of.
Mike, hate to say it you are very much overgeneralizing. I typed up a nice long post on why to use and not use earplugs at one point that is somewhere on this board. Simply put, a FOH guy should use earplugs to prevent damage due to long term repetitive exposure, and should NOT use earplugs to prevent damage due to short term exposure.
What this means....
That is you are wearing earplugs because your ears our ringing after a single concert, you need to look at your setup and what levels you are running at. If your ears are ringing, that means anyone with as undamaged hearing as you are also ringing, and if they are ringing you have already done damage to your hearing. So you are not only damaging your hearing, but also everyone else's.
IF, however, you are wearing earplugs not because your ears are ringing after the concert, but instead because you want to protect your hearing over the long term because REPEATEDLY being exposed to those levels will cause damage, then this is the correct reason to purchase and utilize earplugs.