Of course you are within your rights, but completely lacks any professional integrity. Deliberately criticising volunteers publicly, who are in the same line of work as yourself lacks class and makes you come across really arrogant. We get it, you are good at your job, doesn't mean you have to go around saying those volunteers are rubbish. You'd think anyone in your position would be defending these guys instead of just having a go and saying 'look how amazing I am' think you've made a wrong judgement call on this one.