These companies are contributing to infringement of Broadcom's rights, by selling this equipment.

This is a hazard of dealing with a company known to bully people with their IP lawyers. It's about time they got smacked, and people using their chips should get smacked too for giving them money and supporting them.

Surely this ridiculous and bizarre situation is an end-result of the failure of the US authorities to effectively legislate or enforce intellectual property laws?

It might seem counterintuitive, but it makes sense that the manufacturers using Qualcomm's chips wouldn't have been in the position to know that the chips infringed on a Broadcom's patents.

If it comes to light that you've unwittingly purchased a stolen car, do they let you keep it?

Should they let you keep it, even if the neighborhood gas station complains they won't sell as much gas as they'd hoped to if you aren't allowed to keep the stolen car?

Should we, as a society, stop creating all these examples that say it's OK to break the rules if breaking the rules makes enough money?

Would you say this is roughly analogous to the situation involving Qualcomm (the car thief), the phone manufacturer's (you), and AT&T (the gas station)?