I partially agree and disagree with this suggestion, my points for this being ;
A) I’ve seen some people that have successfully used voice changers in the past to a high degree of roleplay therefore going out of the way to ban the use of it seems a bit extreme, it is a vital tool to some people to disguise their voice.
B) Voice changers can be obtained in real life so removing this element isn’t necessary, say you want to to a high profile crime where you do not want to be identified by your voice.
C) The one part here where I can agree with you is when people decide to roleplay a female, I don’t understand why some will choose to rp as a female but continue to use their normal male voice, but get offended when someone calls them a lady boy or something (Not being discriminating) just stating how I see it.
I believe a voice changer can help in this regard change your pitch or volume of voice to actually make you a female if you wish to rp as one.
I don’t necessarily agree with banning voice changers but I do agree in the aspect of people should at least attempt to form a way of creating accents or different voices for their characters as it something you do not see enough.