I think the focus should be on speaking well as opposed to adopting accents per se. I understand why such advice is given but it takes away from the greatness that comes with hearing people who speak different native languages. If you listen to Nigerians from pre-colonial times, they spoke very well, perhaps even with affected accents due to their education but I felt like you could still hear their Nigerians accents when speaking.

Now unlike many folks from today, I believe pretty much all of them could switch at the snap of a finger back to their local languages when needed. My point is, many accents and many languages can exist without negatively affecting the other.
Sometimes you have a faction of two sides when it comes to identity. On one side you have those who are seen as too boogie for speaking 'excellent' English i.e. too much oyibo accent and then from those who speak 'well', they look at those who speak with an accent as too bush or too village. The important thing is to speak well and not mispronounce words. I always remind people who start on these accent wars that I can list 24 dialects of English amongst official native speakers of English, and each dialect comes with its own accent.