There are arguments to be made for lobbyists being beneficial to the legislative process and arguments to be made that they are harmful to the legislative process. Bear in mind that lobbying is a legal activity, and indeed, is protected by the First Amendment of the United States Constitution, and any argument against lobbying must take this into account. Your opinion on this matter, for or against lobbying, should be a considered one, certainly, so let's look at the pros and cons.
On the positive side, there are arguments to be made. Lobbying is simply the act of trying to influence the legislative process, and this is completely consistent with democratic aims, to allow a constituency to voice concerns and opinions. When you or I write to our legislatures, we are lobbying, within the pure meaning of the word. When a group bands together and selects someone to represent it to the legislature, the dynamic is at least theoretically the same. Legislators cannot legislate in a vacuum in which they have no awareness of what the people want. Lobbying to some degree solves that problem. Also, lobbyists will tell you, and it's true, that they can perform an important function for legislators, which is to educate them. Legislators are expected to make laws in myriad areas, from housing to gas lines, from wage regulation to food safety. They cannot possibly be knowledgeable in all of the areas that they must address, much less have any expertise in them. Lobbyists are quite knowledgeable in their respective areas and often have a certain amount of expertise. The fact that what they do is completely self-serving does not take away from the fact that they can and often do educate legislators, who can then go on to enact statues that are not completely ill-informed. Since every special interest group (with the exception of hate groups or terrorist groups) can have a lobbyist, an additional benefit is that a legislator can be exposed to different and diverse points of view. That, too, is consistent with the aims of a democracy, which are to represent the will of the people, people who inevitably do not all hold the same opinions on matters.
On the other hand, in politics today, lobbying has results that are quite troubling for the state of democracy, since certain kinds of interests have the wherewithal to spend millions and even billions of dollars on this activity, while other special interests do not have the financial means to do so. The interests of banks or the National Rifle Association come to mind. If their interests are in conflict with those of poor people or people who have been victimized by the lack of gun control, there is little money available from these constituencies to hire lobbyists. The interests of the wealthy hold sway in lobbying, with an ever-spiraling movement of legislation that advances their agendas, a vicious cycle that leaves poor people poorer and even less able to voice their concerns and needs. Another example that comes to mind is the dismantling of public education, accomplished at the federal and state level with legislation that has permitted the privatization of schools. This has been effectuated by wealthy interests that stand to benefit from this change. Poor people, many less educated with each generation as our public schools lie in virtual ruins in many cities, are not in a position to hire lobbyists to counteract this movement. So, lobbying has some consequences that are ugly for the majority of American citizens and residents.
Whatever your opinion is on this matter, be sure you support it with good reasoning and examples to help you make your point. My own opinion is that lobbying does more harm than good today, but we cannot make it go away.