I'd prefer an option to have them automatically syphon and destroy what they harvest.
Less about making money more about denying it.
No. That is unbalanced in favor of the siphon owners.
I would never support an automatic loot-and-destroy toggle for the siphon, because that absolves the siphon owner from having to pay attention to it once it's dropped. The entire reason it holds on to the stuff
and can be looted by the POS owner is so that the siphon owner must pay attention to them or they become ineffective in the face of a moderately attentive POS manager. This is balance.
The option to destroy looted stuff would probably be the default use for most players who drop a siphon. Why wouldn't they? Most people using the siphon wouldn't care about the actual loot anyways, or the siphon itself. They just want to disrupt or outright STOP production. With the option to simply destroy looted goods automatically, you therefore require POS owners to form a fleet and clean up the siphons. If you want to completely turn off POS production, the attacker should be the ones to form a fleet and reinforce the POS itself.
People need to realize that these siphons have NO LIMIT for how many can be dropped, and they will likely be cheap and small. Expect 10+ siphons per POS to be deployed in order to shut down production. It's not going to be one single little siphon sitting there skimming the bubbles off the top of the cream. It's going to be draining the whole damn production line.