You're right, the problem with the loans for Cruz wasn't the loans themselves, which are commonplace. He tooled around Texas telling people that he asked Heidi how she felt about putting up all their assets and savings to finance his run for senate - and she agreed on the spot. That was one of his legends that supposedly showed his dedication to the cause.
Only thing is, they didn't put up their assets, they took out a loan from goldman. He didn't declare it before the senate primary because that would have exposed him and his myth. It was no problem to register it once he got to DC - Texans had already bought his story and voted accordingly.
Ignorance. He took a margin loan against his own securities. This has nothing to do with Goldman except for the fact that they were custodians of the account.
I guess you do not understand the concept of collateral?