What do you mean with bad grammars? Do you mean grammars that are hard to parse (require a lot of backtracking) or do you mean that it leads people to creating bad languages?
My experience is that if a back-tracking parser list all the possible terminals it is expecting at the first location (with some additional information about the rules they occurred in) it fails to get passed, that this usually gives enough information to understand what is wrong about the input or the grammar.
My experience is that if a back-tracking parser list all the possible terminals it is expecting at the first location (with some additional information about the rules they occurred in) it fails to get passed, that this usually gives enough information to understand what is wrong about the input or the grammar.