As is well-known among informed drinkers, beers are often cleared using isinglass derived from the swim bladder of fish, usually sturgeon, although not the Scottish variety. Cask ale cleared this way is not suitable for vegetarians, who can't easily work out what beers are suitable for them due to the exemption alcoholic drinks have from nutritional labelling rules.
According to the 2017 CAMRA Good Beer Guide, increasing numbers of brewers are looking at vegetarian-friendly alternatives to isinglass to clear their beers, such as products derived from seaweed, Irish moss (a small sea algae), or silica gel. The Centre for Bio-energy and Brewing Science at the University of Nottingham is investigating using the hop plant as a clearing agent. Guinness announced last year that it would be phasing out the use of isinglass, and quite a few smaller breweries already advertise their vegetarian status. It seems to me that a momentum is building up that will in time render the use of isinglass obsolete, and perhaps even unacceptable, but we're not there yet.
The question remains: should non-vegetarians be bothered about isinglass? I utterly loathe any form of fish or seafood and consequently notice fishy smells even when others can't, but despite that strong aversion, I cannot detect any such flavours in beers where isinglass is used. I've always assumed that it doesn't affect the taste of beer, but GBG editor Roger Protz quotes the opinion of Justin Hawke of Bristol's Moor Beer Brewery who doesn’t use finings at all because he thinks they remove some of the flavour from beer. As a former fairly large-scale home brewer who has made beer both with and without isinglass, I'm not convinced that's true. However, as there are now alternatives to isinglass, I think I'd prefer it if fish didn't have to be killed simply to help clear my pint.
Some people argue further: that we should abandon our expectation that beer should be clear, but I'm not convinced by that either. I'm prepared to accept that certain types of beer are likely to have a haze, but I don't agree that we should expect beer to have a haze as a matter of course. My own brewing experience was that beers will clear without finings, although they might take slightly longer.
Aesthetically, I like the appearance of a clear pint. I understand what some drinkers mean when they say they drink with their mouth, not their eyes, and while I'll go along with this to a point, it is not a general truth. If we don't like the look of what is put before us to eat or drink, we usually don't touch it, which is why presentation is so important in restaurants: a lot of people expect beer always to be clear, which is not unreasonable with most beers anyway, and if that's their preference, they won't find a 'cloudy' pint appealing.
My main concern about the hazy pint is that it can be used as an excuse for badly-kept beer, or beer that is being served too soon. A while ago, I was told that a beer I was familiar with was meant to be hazy when I knew very well that it wasn't. A drinker who is given a poor quality, hazy pint with the excuse that it's meant to be like that might well decide that real ale is not for them and switch to another drink, or perhaps take their custom elsewhere. We all know it happens.
If a beer is meant to be clear, I prefer it to be clear. I'll accept a haze as long as the flavour isn't impaired, especially if it's a style where lack of clarity is not seen as a fault. I am, however, concerned that haziness can be used as an excuse for serving beer prematurely, not looking after it properly, or even foisting beer that's past its best on customers. In such cases, drinking with your eyes is eminently sensible.