My reasons for opposing Universal Background Checks have nothing to do with money. The majority of the time that I sell a firearm, I do so on consignment through an FFL and thus pay a commission equal to or greater than the income or capital gains tax that I'd be charged on the profit anyway. I do this because I feel that it's my personal responsibility to do everything I reasonably can to ensure that I don't sell a firearm to a prohibited person and consigning through an FFL is usually the easiest way to do this.
That being said, attempting to legislate personal responsibility almost never works well. Said legislation is usually either toothless and unenforceable (a straw purchase, for example, can be an incredibly difficult thing to prove) or the measures needed to make it enforceable are so repressive as to become unintended consequences in and of themselves.
In the case of Universal Background Checks, there is simply no way to make such a system work without registration of guns, gun owners, or both. While Universal Background Checks on its face might not seem so unreasonable, registration is a Pandora's box in and of itself. Probably the most obvious example of why registration is a bad idea is the recent debacle with The Journal News in New York. A database of lawful gun owners simply makes it all the easier for unscrupulous journalists to identify and attempt to intimidate them.
The second, and most compelling, reason that registration is a bad idea is that it facilitates gun confiscation by over zealous officials in a time of disaster such as what we saw in New Orleans in the aftermath of Hurricane Katrina in 2005. While that measure was later ruled illegal and several states and the federal gov't later took legislative action to ensure it would not be repeated, it still took many people years to recover their property if ever recovered at all. In spite of the subsequent court rulings and laws, if some bureaucrat decides to ignore the law and try this again, a person's only recourse will be through the courts and that cannot help them when cops and/or soldiers are demanding their firearms right then and there.
Finally, I resent the notion that I should somehow be held responsible for the illegal actions of someone else. If we actually punished crime and treated mental illness appropriately, background checks in general would be unnecessary. I for one am not asking how we can keep guns out of the hands of criminals and the dangerously mentally ill because the answer to that question seems pretty obvious to me. The real question we should be asking is why, if someone is too dangerous to be trusted with a firearm due to a crime they committed or a mental illness, are we letting such a person back into society at all? While I certainly wouldn't trust a convicted murderer or rapist with a firearm, I wouldn't trust such a person with an automobile, knife, can of gasoline, or aggressive dog either. Such people have proven themselves either unable or unwilling to function in a civilized society and the only way to effectively eliminate the danger they represent is to remove them from society through incarceration or, if the crime is severe enough, capital punishment.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar