The bombing of infrastructure isn't that invisible. In fact, it's a well published part of modern US air warfare. So much so it's part of their strategy known as
Warden's Five Rings, infrastructure is ring #3. So it's no secret really, that's what they do.
The thing is, at least in the case of ISIS, it makes sense. Any infrastructure ISIS controls is fair game if that infrastructure allows them to continue their growth. ISIS is far more than just a bunch of maniacal thugs, they're attempting to create a new nation of strict, extreme Islam. For their plan to work they need sustainable revenue. It's no secret that the fight against ISIS is taking more then just a military approach, ISIS is being attacked financially as well with financial dealings with the group being outlawed and their assets frozen when possible. Despite that we know that they've been selling oil and other resources and using that money to buy weapons and stopping that should be key to any campaign against them. So ya, bombing any ISIS oil facilities that they are using to fund their terror campaign should be targeted. And I'm not too concerned about the infrastructure really, the vast majority of the population isn't anywhere near ISIS right now, they're fleeing as fast as they can. The Kurdish town of Kobani was where Syrians were fleeing too, but now most people have or are crossing the border to Turkey or elsewhere. With the place being depopulated, it's infrastructure is valueless to those who abandoned it and only valuable to those who captured it. Bombing it is a no-brainer.
As for Turkey, it's complicated, but I think your analysis is well off the mark. Sure Turkey cares little for the Kurds, they've been fighting them for some time, but they have also been in serious peace negotiations lately and they've been making some good progress. However, Turkish Kurds have warned Erdogan that if Kobani falls, the peace deal will die with the Kurds in Kobani. Meaning, if Kobani falls Turkey may have it's own problems within it's own borders. Remember, it's not so much that Turkey won't intervene, it's also that Turkey is doing all it can to prevent any Kurds from helping those in Kobani. No resupplies and no re-enforcements which is probably the real reason Turkish military units are in the area - to stop the Kurds, not so much ISIS. Erdogan is trying to pressure them and using Syria as part of his negotiations with the PKK. Erdogan doesn't want a Kurdish nation to take hold anywhere and thus he has a great incentive to do nothing. But still, not all of Turkey thinks like Erdogan and there have been protests and I heard today even shootings involving Turkish Kurds and Turkish police. There are protests in Turkey in support of Turkish intervention so it's hard to say how things will pan out.
And as for the Kurds joining ISIS? That's funny, I hope you meant that as a joke. Even if the Kurds would consider it after the recent murders they suffered at ISIS hands, ISIS would never even consider allowing the Kurds on their side. The two groups both wish to create a new state, one based on ethnicity and the other on religion. You seem to think that the old proverb of
the enemy of my enemy is my friend holds up in the middle east. The fact is the Kurdish peshmerga are the only ones that could stand up to ISIS and even then only with some kind of air support. The hope is that Kobani can be reconnected with other Kurdish areas along Northern Iraq but for now ISIS and Turkey stand in the way.
As for attacking Assad, again you're wrong. In a recent interview with an FSA officer who opposed the ISIS air campaign, he stated that getting rid of Assad would be more productive in eliminating ISIS. He argued that ISIS is tolerated and funded only because they are fighting against Assad. If Assad were to be taken care of ISIS would no longer have that pull - it's recruitment and revenues would shrink. The only places ISIS has been tolerated are Sunni strongholds and even then ISIS is on it's best behavior because it seems the only thing they fear right now is a Sunni backlash. In all other areas they have resorted to mass killings and raping and the general depopulation of entire areas. That same FSA officer said that with Al Nusra, they can smoke and curse in front of them and they do nothing. They can agree to disagree and even discuss their differences. But with ISIS, if they think you're different they cut off you head. ISIS can't survive without at least some popular support and with Assad gone the Sunnis will have no reason to tolerate them.