There is a world of difference between being "uncultured" or rough in speach, and being rude (ie. in the sense of slandering others and using unbiblical insults) or crude. One is just the person's personal style - which should never be the basis of our critiquing of his message - the other is sin. The Bible quite clearly teaches us to guard our tongues, not be crude in our speach (can't remember the exact terms used right now), and that we will give account of what we say to others.

The Bible also tells us to judge people by their fruits - doctrine and words are fruit. We are commanded to expose what is wrong - that would include exposing rotten fruit when it shows up.

Ephesians 5:3-4 But fornication, and all uncleanness, or covetousness, let it not be once named among you, as becometh saints; Neither filthiness, nor foolish talking, nor jesting, which are not convenient: but rather giving of thanks.

Ephesians 5:11 And have no fellowship with the unfruitful works of darkness, but rather reprove them.

Funny how some reprove those who are reproving sin!...