Allowing the body to inhibit severe reactions to psychologically damaging events can be seen to be a positive thing. People suffering with PTSD, for example, aren't able to have a good quality of life. If propranolol can reduce stress and improve functionality, then I believe it should be an option for those in psychological pain.
In certain cases (for example post traumatic stress) it is perhaps beneficial to mental health, but certainly shouldn't be a regular practice to wipe away all bad memories. We need all our memories to learn from, and because they are part of who we are.
Wiping away anything bad is also much to close to attempting to obtain oblivion through drugs for my comfort.
No. A person's memories are part of their life experience and who they decide to become. If we have the ability to erase those memories, a person would not be able to learn from those life experiences. So often, we reference a particular memory with a particular action, and our minds are so much complex than science can understand. If we start tampering with the unknown, it will lead to much more bad than good.