This is absolutely true in America and in almost no way is it necessarily tied to being a Christian, even those who are non-religious will often espouse the fact that alcohol "isn't like other drugs". Obviously this is just anecdotal evidence but a number of people I know will insist, for example, that alcohol is far less harmful and "not a drug" when compared to marijuana. They usually use an example of someone they know who they know uses / has used marijuana, who clearly has issues / problems in their life and say, "see what it can do to you", while completely ignoring X number of alcoholics all around them that have completely fucked up lives and the fact that the person they are talking about often also abuses alcohol so there is really no way to separate his / her alcohol use from their marijuana use to pinpoint which has a more negative affect.
The scary thing here is that basically no one in the U.S., who isn't a teenager / in college, will openly come out and say to most people, "I smoke marijuana", so anyone who is remotely normal / has a job, etc will only tell other people whom they know also smoke marijuana (even if just occasionally), because otherwise they are ostracized. Therefore, we have this skewed perception where only people who are either too close to someone to hide it (such as a son / daughter) or there life is messed up in such a way that its obvious / they don't care about hiding it are the ones that these people can point to and say "they use marijuana" as any "normal" person who uses it will never admit to it around someone who they know is against it or even neutral / not in favor and may actually go to great lengths to hide it as the repercussions can be extremely severe. If you live in the wrong state, you can quickly lose your job, etc very fast if word gets out.