It makes it more difficult to design really thin phones because the battery needs a sturdier case and an additional connector to be easily replaceable. Generally making a phone smaller and thinner makes components less accessible. Personally I think it is more important that high quality batteries are available for a long time. In my opinion it would be fine if some tools were required to replace the battery. Ideally that only needs to be done once every 2-3 years so if it takes a bit longer it isn't such a big deal as when there aren't good batteries available.