Here's another perspective. If one places a call and someone answers the phone, you know they answered it - the phone stops ringing. If they don't want to answer it, they don't. Read receipt is merely the acknowledgement that someone has viewed the email, like someone answering a phone. There's no privacy issue here. A read receipt doesn't mean that they actually read the email, understood it, agree to it, etc. Perhaps instead of implementing a "read receipt" one can implement a view receipt?
Here's another perspective. If one places a call and someone answers the phone, you know they answered it - the phone stops ringing. If they don't want to answer it, they don't. Read receipt is merely the acknowledgement that someone has viewed the email, like someone answering a phone. There's no privacy issue here. A read receipt doesn't mean that they actually read the email, understood it, agree to it, etc. Perhaps instead of implementing a "read receipt" one can implement a view receipt?