It is legitimate to question the findings of the survey in this particular instance, without attributing malign motivatons to those who do raise the questions.
The authors of the report themselves highlight problems with the survey; A large proportion of the respondents come from Manchester;The respondents were self-selected; Its a questionaire based survey, so no way of checking the veracity. There is no control group either - they have referenced figures derived from the British Crime Survey -and there is no direct age group comparator, so the figures are adjusted.
Here is what the authors themselves say;
The standard source of information about drug use among the general population is the British Crime Survey (BCS)
. The BCS is a general household population survey using a
representative sample of 16-59 year olds. Making comparisons between the drug use reported by the POTP respondents and that reported by the general population is not straightforward because the POTP sample is younger by comparison.
So, whilst it may well be an accurate enough survey of attitudes amongst this particular age group of the LGBT community, it does not really offer a particularly good direct comparison with a similar age- group who are not members of the LGBT community, since they did not survey this group.
http://www.lgf.org.uk...ar_3_ReportFINALL.pdf