I personally group weed and alcohol together, it's something DP and I cannot agree on. IMO, if you treat alcohol or weed properly, i.e. do it moderately, not around children, do not get so wrecked you can't care for any kids that you are responsible for, do it every now and then rather than every night, etc, etc, then there isn't really a problem.
However, cocaine, speed, heroin, ecstasy, shrooms, can kill you with one hit.
I have taken all of the above at some point in my life, before children and have lost a number of friends to heroin, I have watched an exbf be bought back to life after a dodgy pill, that he got from our regular dealer, that our regular dealer got off his regular dealer and so on.
My exp took cocaine 'recreationally' it cost him his partner and children. He had it 'under control' he only took it when he went out, but everytime he went out had to have it, th state of him the next day was terrible, and that goes for drinking too.
If you are going to be looking after your DC's the next morning you shouldn't get completely rat-arsed, nor should you get fucked on drugs. Though drugs are likely to keep you awake to stupid o'clock and alcohol knocks you out, so in theory you have longer to sleep the alcohol off.
Also, as someone said earlier, of course legality is an issue, if you get knicked in possession of a class A drug, you could possibly lose your job, if you have too much on you, it's intent to supply and you're in even bigger trouble.
Hope that little high you get on a night out is really worth your kids seeing the front door kicked in cos the police belive you're a dealer, or growing up without parent becuase one is dead or in prison.
Really responsible.