Starving the defenders means starving the civilians too, and that's unacceptable.
In modern times at least, but the whole point of a siege is often to simply outlast the enemies food (and possibly water, if it can be choked off) supplies.
I know what a siege is. If the civilians actually belonged to the defenders, it would be another story entirely, but that's not the case here. Not everyone in that city is friendly with the rebels.
I was under the impression at first that the Russians and Syrians were actually helping these people, but they're not, they're just attacking. Fair enough. That's probably the best way to help these people. Apparently the rebels are also actively
preventing people from leaving and going somewhere safer.
This doesn't seem like a situation where you could actually supply these people who are cut off seeing as how apparently everyone who could leave has run away (around 100,000 people), but allow me to explain my position anyway. My stance earlier was that, given a situation where you can either:
A) Starve the enemy, but also starve civilian hostages who don't support them, and in return you win faster.
B) Supply the enemy, but keep civilians they have hostage from starving to death, and you prolong the battle.
I would choose B. The key word for me here is
hostage. These are not the enemy's tax payers, they're bystanders. If the civilians are undeniably on the enemy's side, and they're not fleeing when they know combat is about to happen because they can't or don't want to, they don't deserve to be killed or raped when you take over the city, but if they starve as a side effect of winning the battle and not any direct action, then that's as acceptable as things get when it comes to war. That's how I'd prefer they die; only after all reasonable attempt to keep them alive without undermining the conflict too heavily.
Meanwhile, in the real world, the enemy is trying to work the hostage tactic and the Russians are bombing them anyways, and both sides get to look bad. Oh well.