I don't need the extra security provided by end-to-end encryption for the vast majority of emails I receive and send. I value that ability to search/filter these emails far more than I value the security. For the few emails I send where the value of the security provided exceeds the lost value due to being unable to search I can, using their extension, enable end-to-end encryption. This system suits my needs perfectl…
One email sent the wrong way when tired. One change in legislation (to e.g. retrospectively criminalise an activity or legalise a certain type of snooping). Now your company's IP is compromised. Or now your in jail. Or now you can be blackmailed.
Furthermore the idea that you will be encrypting the mail may cause tired future you to write something you wouldn't put on a post card.
So unless you are perfect and never ever click in the wrong place good luck in this brave world of ours.