Tell them that EVERYONE puts the weight back on with EVERY diet if they go back to the way they were eating before they went on it.
The latest research is that it is not unsafe to lose weight quickly. In fact losing it quickly has been proved to be more successful. If you only lose a little a week, you end up putting it all back on at the least little lapse, whereas with LL you have lost stones before you might have a little lapse and then when you put on for that lapse is a very very small percent of your weight loss. Therefore it is easier to control.
Also, there has been research on diabetics (type 2) to show that with a VLCD you not only lose fat round your body you lose the dangerous fat round the heart. They went back to these people 14 months later to see how they were. Some had indeed put their weight back on, but they found that the fat round the heart had not come back.
People tend to be more sympathetic if you say it is for health reasons (no need to explain your condition).
I loved what Pauline Quirk said when people started telling her she was looking 'gaunt'. She just replied "good".
So if anyone tells me I will have saggy skin I will say "can't wait" or "and what have I got now - saggy skin with a lot of fat underneath" If the person who says these things is a lot lighter than I am (which most are at the moment) and they are kind and mean well, I will say that I am trying to get down to their size, because it looks so nice
I would also ask on what do they base their prejudices, and then have sufficient knowledge of LL to be able to answer them sensibly.
But I am doing this for myself, not them or anyone else.