The strength of marijuana has increased dramatically recently, you can not think that your parents generation smoked it and turned out fine. The strength has increassed about 66% in 12 years with over one third of marijuana users addicted, which I'm thinking you don't want to be, (source:
http://www.newscientist.com/article.ns?id=dn4954)
Now marijuana has a number of side effects which really come into part if you plan on doing it regularly,
You are more likely to develop psychotic symptons later in life, particularly if your family has a predisposition, in the study 21% of marijuana users experienced them compared to 15% of non users, with predisposition this is 51% and 26% (source:
http://www.newscientist.com/article.ns?id=dn6745)
It can cause infertility.
No matter what you said about not wanting to be told its a gateway drug, it is, no other environmental or genetic factors have been found that suggest that it is only in certain people (source:
http://www.newscientist.com/article.ns?id=dn3291)
And smoking it is more harmful then cigarettes (source:
http://www.newscientist.com/article.ns?id=dn3039).
It is your choice as to what is more important, but at least undersand what you are doing to yourself first.
Ecstasy is one of the worse to use, not because of the affects of the drug, but due to the constituents of the pills, it can often contain a cocktail of drugs inside it.
Taking ecstasy while still under the affects of marijuana can double the short term memory loss.