This is another take on the Encouragement vs. Pressure issue:
Bad Suggestion: You love peanut butter? You should try switching to almond butter.
What makes a suggestion good or bad has nothing to do with the suggestions itself; it's about how the suggestions are given. In the good suggestion, the person is not saying that their friend should stop reading Harry Potter - they are recommending another series that their friend might like, in addition to Harry Potter. In the bad suggestion, the person is telling their friend to "switch" to almond butter, which means eating less peanut butter. Unless the friend said that they were looking for a substitute, it is not logical to assume that someone who loves peanut butter wants to stop eating it.
Good suggestions add to what a person likes, and are based on what you think they might enjoy. Bad suggestions replace what a person likes, and are based on disapproval of what they do, and what you think they should do instead. The exception is if a person tells you that they want to quit doing something and would like advice, in which case a helpful suggestion would be good.