I had worked in four labs (two summers, a summer+school year and then full time during 2 year gap before grad school) when I applied with diverse aims (pharmacology, developmental genetics, bioinorganic chem, and pharmacology). At my Einstein interview (a biomedical sciences PhD program), one professor was very skeptical and concerned that I was flighty and not committed. When I explained how the diverse experiences tied together and lead me to a firm conclusion of what I will study for my thesis, he understood that the experiences were an asset. The other professors I spoke to were glad to see my diversity of experiences because they saw it gave me a deeper appreciation of academia. My passion and ability to adjust to new problems were also assets. So, you might encounter some haters, but just emphasize how much you have learned in the process. Also don't say anything negative about the experiences (like everyone quit the group, or I found the new project direction boring) as they can reflect poorly on you. The adcom doesn't know if you're telling them the whole story and might guess that problems follow you. Instead emphasize positive reasons for switching (like, I enjoyed the synthetic approaches, but found a great opportunity to explore computational chemistry so I decided to switch).