Well if their both pastors...

God indicated all the seed-bearing plants are good
on literally the very first page of the Bible
(see Genesis 1:11-12 and 29-30)

It is no accident Christ, God, The Ecologician,
Created seed-bearing plants and said they are good
On the Bible's first page. The only biblical restriction
is that it be used with thanksgiving. (I Timothy 4:1-5).

The bible is all about black and white, no grey areas (especially the Old Testament). If god says seed-bearing plants are good, they're good - though don't let your parents convince you that if you smoke, it has to be shwag - this could be tricky.

Also, marijuana is proven preventative for Alzheimer's. This is a recent study that just came out, so you shouldn't have a problem finding it. Marijuana also DOES effect short-term memory loss, it DOES NOT effect long-term memory loss, and when you quit, your short term memory comes back.

If they are worried about your lungs, tell them you'll vaporize...

There is a difference between smart stoners and stupid stoners. Stupid stoners are the ones that get high all day everyday, and when their weed runs out and their rent is due, they start thinking, “How can I make money to pay for my habit and other bills as well? I know, I’ll sell drugs!” These people end up in jail or continue to contribute nothing to society except a place to score. Smart stoners realize there is more to life than smoking weed, and toke responsibly. They get jobs, don’t get too fucked up to work (if it all), and when their day is done and they have the funds, they’ll score a sack to smoke up. Stupid stoner tokes up the previous night, and right before a final exam, and fails miserably. Smart stoner studies all night, takes exam in the most beneficial frame of mind, and celebrates with a sack at the end.

Don’t let your parents think everyone is a stupid stoner. I graduated from an ivy league school and am now in one of the top 10 careers in America. Another stoner friend from high school just passed the NY bar exam. Another graduated college with a double major 4.0 (mathematics and economics), and now works in an executive role in one of the largest insurance companies in the United States. I also have another friend that dropped out of school and now mows lawns and coaches 9th grade football, and yes, it’s because he couldn’t stop getting high and start going to class.

And, if all else fails, and you know you aren’t going to get what you want, have some fun with it. Tell them that weed lowers your sperm count, and if you stop smoking, you’re going to have to start having anal sex with your girlfriend to avoid her getting pregnant. They should remember what happened to Sodom and Gomorrha and want to prevent the same fate from befalling you.