Taking marijuana affects and stimulates thinking and leads to a philosophic, positive life attitude. It causes an euphoric feeling. You start feeling very happy and it stimulates your mind. Someone who is "high", has a positive view on the world and on life.
Marijuana doesn't cause any mental harm. There aren't any cases known of persons who are crippled for life, neither physically, nor mentally, but marijuana can intensify latent, suppressed fears, that were already existing.
In the Netherlands marijuana is mostly smoked in a joint. The hash or weed is crumbled on some tobacco and sometimes covered with even more tobacco. Then a big joint is rolled, often very ingeniously, and it is shared by a number of smokers. The consequence of mixing tobacco and marijuana, is that the smoker does get STONED, but not HIGH. Being stoned is a pleasant form of a light daze. The smoker feels dreamily, his/her world slows down, music becomes more intense and thoughts expand enormously.
Someone who is stoned is not very keen. Why should you worry when you're feeling so fine?!
There is a large variety in the effects of the different sorts of marijuana. The experienced taker knows the difference between Nepalese, Turkish, Afghan or Moroccan hash. Some sorts make you light-footed and talkative, other sorts prompt to lie down and dream.
In some circles alcohol is taken while smoking a joint. Mostly beer, sometimes wine, but real macho's also drink whisky or another spirit while smoking their joints. Then smoking marijuana is useless, as alcohol breaks down the effect of the THC.
The reason why marijuana is so popular, is dead simple: everyone who smokes marijuana regularly, knows from personal experience that it's harmless. Innumerable scientific researches have proven again and again that taking marijuana is not addictive.