When someone feels threatened and intimidated, they will seek out petty reasons to try to tear someone down. Katy is a successful woman, so people will say whatever they want to justify their reasons for disliking her. In many cases, it is as simple as seeing other people doing it and wanting to fit in and be popular.
People did it with Gaga, they've done it with others in the past. It's an evolutionary cycle. During their peaks, Celine, Whitney ,Mariah, Birtney and others have had similar negative garbage said about them. People like to see others succeed to a degree. There's an old saying and lyrics about building a person up only to tear them down. It's Katy right now, next year it'll be someone else. It's just the nature of the beast.
Listen to Katy, love her music and appreciate it as a fan or dislike her doesn't matter. Don't worry about what others have to say about her. If they feel they need to justify themselves with their antics, let them. At the end of the day nothing anyone says on an internet forum will stop the sun from rising or setting.
This alone proves how basic she is 
