It's very hard to accidentally give a random guy access to your Gmail inbox. Doing so would require you to opt in to a dialog clearly and explicitly stating that you are giving said permission to a developer.
Access to my personal email would be pretty much security game over for me as far as I can tell. Other people might feel otherwise.
This throws up all sorts of red flags with us, but not with most people. It's easy to not realise what's going to happen here.