One of the key policy objectives of Western governments over the last twenty years has been to "fight the war on drugs". However because there is no clearly defined foe and because of the enormous amounts of money and extremely high profit margins that can be made from selling narcotics in the US and Europe it has so far proved impossible to stop more than a relatively small percentage of the large amounts of narcotic drugs shipped from the third world into the first world countries.
As a result the criminal gangs that control the drug trade have access to funds and resources equivalent to those available to third world governments. The danger for the west is that increasingly terrorist organizations are using the drug trade in order to fund their own campaigns; this has been the case in Afghanistan, Latin America, Lebanon and Northern Ireland. Outcast governments, like North Korea, have also profited from the trade.
For the west the drugs trade represents a threat that is probably more serious than terrorism, and because it so frequently funds terrorism, the two threats are intertwined.
Drug money is now one of the major sources of corruption, and the trade itself undermines the social and political fabric of any country where it gains a foothold. Western governments are reluctant to take the necessary measures to prohibit the importation of drugs because the security measures are expensive, and because many left of center governments see targeting of the groups who supply and distribute specific drugs as racialist. For example Jamaican "Yardie" gangs import and distribute drugs in the UK, but there has not been effective action to ensure that gang members do not enter the UK or to restrict their activities once (illegally) in the country. In the case of the so-called "soft" drugs some politicians have memories of their drug use at university, or are aware of the current drug use of their immediate circle of friends and do not see drug use a s a serious threat.
There are actually two separate aspects to the drugs trade; one is the effects on individuals of the use of drugs, and this is well-documented, the second issue, which is more important politically is the criminalization of the drug trade and the creation of immensely profitable criminal organizations. The situation in the west is now so serious that some people are calling for the decriminalization of all drugs in order to remove the income streams of the criminals and terrorist organizations who profit from the drug trade.