Amongst socialists back then there was a big prohibition movement. The Scottish Prohibition party, who had one MP until the 30s was a firmly socialist party and there was a form relationship between the Temperance movement in The UK and Socialist ideals. Basically the reason was because they saw alcohol as a tool against the working class wherein the ruling class kept them addicted and drunk to prevent them from self improvement while making money off them.

Even today, a lot of Anarchists are straight edge for similar reasons, plus the idea that drinking and drugs means they close control of their faculties and this, autonomy.