If politicians were banned from pursuing their own outside interests it would make for a better government and society would be well off for it. When politicians go for outside interest they can invest whatever tax payer money into the idea that they were given jurisdiction over which can be seen as a waste of money.
While in office, politicians should be banned from pursuing outside interests to avoid any insinuations of conflicts of interest. Elected officials are in the public trust and their position is usually paid or compensated in some way. Federal officials especially, with perks and a salary, should be banned from pursuing outside interests as their policies can affect any companies they influence.