Biodegradable plastic has its own issues as well. Nearly all of them are food-based and will set off one food allergy or another, plus you may also have issues with straws dissolving in hot liquids.
Someone elsewhere in the thread mentioned straws made of lobster shells. In addition to shellfish allergies, such a straw isn't going to be suitable for anyone who's vegan, and I wouldn't be surprised if it wasn't kosher either (TBH, I'm Jewish, but I don't keep kosher, and I don't know enough about the laws of kashrut to say whether or not drinking out of a lobster-shell straw is equivalent to eating lobster).
Hard to drink hot liquids with a straw anyway (stirrers are another story).
The plastics I'm think of are PLA and PHA. Mainly made of corn, but you could synthesize them from pure chemicals as well. Far more common than these "lobster shell" ones.
Honestly, even in cold liquids, I'd be worried about non-plastic straws getting soggy and/or melting if left long enough.
I haven't specifically looked into PLA and PHA much, but a quick google sees PLA being referred to as "too good to be true" and having "misleading biodegradability". I'm not seeing such concerns about PHA, but I've also only spent like a minute looking it up, and I wouldn't be surprised if some more intensive searching turns up some serious drawbacks. I have turned up some concerns about bioplastic production competing with food for the same agricultural resources, though.
PLA really needs an industrial composter to break down fully, but this is still better than traditional plastics. It's just polymerized lactic acid, which is common and naturally occuring in the human body.
PHA generally breaks down faster in the natural environment (i.e. it's biodegradable, not just compostable) and it has similar properties to PLA.
Straws use an absolutely minimal amount of material. I really don't think concern over agricultural resources is valid for such uses as it is compared to, say, the massive amounts used for biofuels. And of course, it's not as if metals have no resource requirements, either.
A typical straw weighs about .42 grams and thus uses about as much agricultural material as two kernels of corn (about as many calories as two tic tacs). That's not the problem, here. To put that in perspective, the energy in that straw (about 0.005 kilowatt-hours) is less than we just wasted arguing about it online.
Someone elsewhere in the thread mentioned straws made of lobster shells. In addition to shellfish allergies, such a straw isn't going to be suitable for anyone who's vegan, and I wouldn't be surprised if it wasn't kosher either (TBH, I'm Jewish, but I don't keep kosher, and I don't know enough about the laws of kashrut to say whether or not drinking out of a lobster-shell straw is equivalent to eating lobster).