You're right, of course meeting with legislators shouldn't be made illegal. What's happened is that the term "lobbying" has been misused to include all of the related activity that goes along with lobbying these days. Typically, very large campaign donations accompany corporate lobbyists.
There are also occasional favors that avoid the whole bag-of-cash problem.
Perfectly okay: A lawyer hired by a large corporation going to Washington and saying, "Hey, Mr. Senator, we should talk about this legislation that could affect the company that hired me."
Not okay: A lawyer hired by a large corporation going to Washington and saying, "Hey, Mr. Senator, we should talk about this legislation that could affect the company that hired me. How about we meet at a golf course in the Caribbean?"