Buckley was 'way out in front of the "conservative" movement on this issue. He was actually what we would call a libertarian these days. I am fiscally VERY conservative, and would like to shrink government spending and taxation as responsibly as possible, and I found myself agreeing with Buckley on many issues, just as I found myself disgusted by the neo-cons who managed to hijack the GOP.
The Republican party would strenuously resist any attempt to de-regulate the cultivation, sale, and use of marijuana, and would use any such attempt to paint proponents as "druggies", "soft on crime" or much worse. As is often the case, their rhetoric would be 180 deg off the mark, because taking the funding (marijuana distribution profits) away from the gangs would make inner cities safer, and free up law-enforcement to engage in activities that actually protect citizens.