How is voice or video chat "unprofessional"? If anything voice-chat would be considered a professional feature since it'd be the internet equivalent of a conference call. More to the point though, what does it matter to you if other people use mIRC for non-text chat? The word "chat" isn't specific to text, it's original meaning would of course be to chat as in a conversation - one using voices no less! Even if it were, it's also not called Internet Relay File Transfer, yet DCC SEND is still included because it's useful for sending the odd file to someone you're chatting with and is a worthy addition used by many IRCers (that's chatting IRC'ers, not filesharing IRC'ers) - "useful" being the operative word.
Remember video and voice chat would not affect you in the slightest if you didn't choose to make use of it, it'd naturally be implemented as DCC sub-protocols so all you'd have to do is set mIRC to ignore those requests and it'd be as if it were never there.
