Is balance/proportionality desirable? In all things or only in some things?

It's undesirable if it's not thought through properly; because then the drive for "balance" skews reality.

It's a problem many journalists face when trying to give both sides of a contentious matter. Often, they find most or all of the genuine experts are on one side; leaving them no choice but to interview ignorami on the other in the name of "balance". They have presented both sides of an argument but the balance is purely between pro- and anti- by numbers of interviewees rather than of opposing evidence on both sides of the argument.  Consequently it comes down to who has the more persuasive way with words rather than facts.

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This has a very strange parallel in political and social affairs.

BBC Radio Four carries many analytical programmes, and when trying to highlight when something has gone wrong somewhere and to work out how, without blaming individuals, the producers invite interviews or at least explanations not only from the plaintiffs, but also from the accused organisations or in the case of governmental departments, sometimes the ministers overseeing them. 

The fault in such cases is very often by mistakes, badly-designed or over-loaded processes, not malice. Yet all too often the journalists are met by corporate or departmental cowardice, fobbing the programme and its listeners off with "no-one is available for comment", or just blunt refusals; though sometimes accompanied by a message anodyne and uninformative enough to be a "mission statement".   So we learn all about the effects on the  victims,  but not always what the organisations concerned might or will do to put things right. 

The programme-makers are doing their best to be balanced and give both sides the chance to present their case fairly, but are prevented from doing so by the one side you'd expect very keen to give its side of the story!

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If you mean "balance" in social, racial, religious, cultural, etc.  mixes, the lines become very blurred and messy indeed, and many people plump for simple numbers-games as the easy way out.

An odd UK example of that has been mutterings about outdoor-activities, public guided-walks etc. in areas like the National Parks being supposedly "exclusive". (They are financially if you want to live in them, by high house prices; too high for many locals.) 

Our National Parks are not wildernesses-in-aspic. They are rather like the Regional Parks in France: large areas of beautiful countryside, almost all farmed, containing villages and small towns, light industries, tourist-related businesses, served by roads and in some, railways,  criss-crossed by public footpaths; so are hardly exclusive. Some, especially in the North of England, are very close to major cities, too.

However, apparently they do not attract many tourists from the ethnic minorities, so those people are under-represented there by population proportion alone, so what are we to do about it? I believe some guides in places like the Lake District became so fed up with the implicit but false accusation that they have resigned.

It's not a question of proportion or quotas or balance. These places and services are open to all, and if some don't visit it's either because they can't afford to travel, or are simply not interested - whoever they are, wherever they live, whatever their background. The Numbers Gamers do not ask that, though: all they consider is artificial balance-by-category. All that really matters, is that the opportunities exist for all - and they do; the only obstacle being lack of spending-money, and that can stop anyone, and often does.

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  Being  balanced or proportional is all very well,  but like a balanced diet or balanced working-life, only works if applied in a thoughtful, analytical way.