‘You can, but why would you?’

Explaining matters of ‘taste’ to my children is, I expect, going to be a minefield. I want my kids to be free to have opinions, and to voice those opinions even if they are controversial. So how do you explain that some things are ‘in bad taste’ without basically saying ‘I (your parent) don’t like it’, or ‘The majority of society doesn’t like it’ and therefore it is ‘wrong’?