If lobbying were abolished, there would be a number of consequences. In general, the power of interest groups would decline and the power of parties would rise. The system would, however, be arguably less democratic.
Lobbying gives interest groups a great deal of power. It allows them to be in touch with members of Congress on a constant basis. They can spend a great deal of time trying to persuade those members to support their agenda. If they were not allowed to do this, the interest groups would lose power as they would not have such constant contact with the members. Political parties would gain power because they would not have to compete with the interest groups for influence. For example, Republican lawmakers might be more likely to listen to their party leadership rather than to the National Rifle Association.
Many would argue, however, that such a system would actually be less democratic. We think of interest groups and lobbyists as something of an evil, but they are actually representing the opinions of many voters. When the NRA lobbies, for example, it is making the wishes of its constituents known to the members of Congress. This is vital to democracy. People need to be able to communicate their wishes to Congress if they are to truly be in charge of the government.
So, while a ban on lobbying might seem like a good thing, it could well reduce the amount of democracy in our system.