In the UK there is also,unfortunately, a class aspect to regional accents. Whilst this may have weakened in the course of recent decades I suspect it still lingers on.
There was, during WWII, an occasion when the BBC, wanting to promote national solidarity, decided to get the Lancashire entertainer Wilfred Pickles to read the 6'o' clock news, Lancashire accent and all. This only happened once. The Beeb was inundated with complaints from the upper middle class denizens of the 'Home Counties' about 'unacceptable, uneducated, unintelligeable regional accents','Not the King's English' and the like, from people who considered that, north of Leighton Buzzard and Welwyn Garden City, the country was the preserve of the great unwashed, uneducated proletariat who were incapable of 'speaking proper' and whose accents were not simply unacceptable but completely beyond the pale. Regional radio and TV comedies have redressed the situation somewhat, but I suspect that, in some circles, this attitude is still present.
On the subject of mutual understandability, there was, long long ago, a TV comedy show in Scotland starring Stanley Baxter. He did a wonderful skit on the then current fashion for foreign language learning programmes on the Beeb entitled 'Parliamo Glasgow'. Totally impenetrable over the top 'Glesga' dialect/accent with subtitles. Hilarious.
To be serious though, this can happen in real life. Not long after I'd moved to Germany I watched a film about a successful anti nuclear power station protest near Freiburg in south-west Germany. The local dialect there is very strong and, for outsiders, scarcely understandable. The film had (high-)german subtitles, something I hadn't reckoned with.
For me ,it's not about acceptable or unacceptable accents, extra consonants or not, it is simply about being aware that there are situations where it is preferable to tone down the accent, play down the extra consonants.
Any body remember Martin Carthy's late 60's vocals.....? And Dave Burland's wonderful parody of them?