1st the post that were removed were not about people even talking about plastic being good or bad they were actually talking about voltron, john and kate plus 8 the yankees and micheal jackson so your not missing anything.
2nd pet stores (even ones that are didicated) are looking to make money and in order to get the most income as they can they put animals where they can be seen the best and tanks do that well just like grocery stores putting the sugar cereals at kids eye level people want what they see..... out of site out of mind people like to buy on impulse.
they also like to put more animals in smaller tanks than they should be in more tanks with more animals in a smaller area means more money that they can make. this is one of the reasons you hear alot about not buying animals from pet stores they are not kept correctly. pet stores are also most times are bad places to get advice on keeping your pet. if they can sell you $100 worth of stuff that you dont need even if its wrong they will.
do you know the exact rate to which these fumes accumlate in an area and how much air movment is needed to keep the air at a level that is healthy? if you do then we can figure out if we are ventilating enough. ive seen no post on any website about snakes or any animals passing away from platic fumes so im gonna go out on a limb here and say that 1 there probably is a way to vent and 2 that pretty much everyone useing tubs is venting enough.
also know that with snakes they dont breath the same as us so even in a area that we couldnt breath snakes would be just fine thats why you dont see people using a gas chamber to put snakes to sleep like you see with rats.