George Eliot does much more than just suggest how Silas's love for gold is a bad thing. From the moment that he begins the collection of his gold, until the cruel theft of it, the reader can see how Silas has become even more alienated, more antisocial and even more isolated than ever as his obsession grows.
It is even more clear in chapter 5. When he finds out that the gold is gone, his reaction is so violent that there is no doubt of the hold that the gold had in Silas's heart and soul.
The sight of the empty hole made his heart leap violently, but the belief that his gold was gone could not come at once—only terror, and the eager effort to put an end to the terror.
Silas had been keeping that gold, not because he needed it extremely badly, but because he had become blinded by greed. He enjoyed staring at the gold much more than thinking about how to spend it. Moreover, he had developed an unnatural relationship with it, meaning that he basically depended on its mere presence for his happiness. However, the absence of it causes a very bad nervous breakdown that can only be compared to taking a really addictive habit away from someone.
Again he put his trembling hands to his head, and gave a wild, ringing scream, the cry of desolation. For a few moments after he stood motionless; but the cry had relieved him from the first maddening pressure of the truth.
We know that, ultimately, the breakdown that Silas suffers will make him a better person. However, it is by seeing the effects of the theft on Silas that George Eliot tells us exactly how bad was the dependence that Silas had to it.