I only knew that smoking is bad for our health. Didn't know that it is bad for our spiritual practice too till I read about it here.
According to the Gelug Master Zopa Rinpoche: Tobacco is a very impure plant, it came about due to devils, who made prayers to harm people. Then, from that, tobacco grew, to harm people. Especially, it blocks spiritual development. If spiritual development doesn't happen, then one has to continually die and be reborn, and experience continual suffering and problems, again and again, without end, as human beings, hell beings, devas, animals, etc. There is no end to the suffering in samsara and, also, you can't liberate thousands of others from samsaric suffering, and bring them to full enlightenment.
I strongly support Thailand's move to ban smoking at religious places.