You are conflating the investment banker and the equity research analyst, which have legally mandated information sharing firewalls. Also this potential conflict is clearly and openly disclosed, e.g. "This company publishes research and also seeks to do investment banking business with Tesla".

Further, Goldman conducted a secondary share offering for Tesla as recently as summer 2015, so it was exceedingly obvious to anyone who makes investment decisions based on the research that this conflict exists.

I have worked at several wall street firms and also worked for firms in silicon valley, and I frankly noticed more numerous and blatant conflict of interest situations in silicon valley.

EDIT/UPDATE: Prominently displayed in large font on page 1 of the Goldman research report on Tesla:

"Goldman Sachs does and seeks to do business with companies covered in its research reports. As a result, investors should be aware that the firm may have a conflict of interest that could affect the objectivity of this report. Investors should consider this report as only a single factor in making their investment decision."