Bitcoins, just like other forms of money, should be taxed by the IRS. It is necessary for the government to collect taxes from their citizens. Digital currencies like Bitcoins should not be a way for people to avoid paying taxes. The IRS should find a way to modernize their tax system.
Taxes are meant to pay for public services that are externalities and to pay for specific agencies. What compelling reason is there for the IRS to tax bitcoin? Bitcoin does not cost the U.S. money to print or trade with, and the U.S. can get tax money from dollars used to purchase bitcoin (as those dollars have been taxed as wages or salary).
No, Bitcoin should not be taxed by the IRS. Since Bitcoin is a virtual currency that is not currently regulated by any government entity, it would not be appropriate for the IRS to tax it. Bitcoin's value fluctuates widely within short periods of time. This fluctuation would make gains and losses experienced by investors nearly impossible for the IRS to track. The IRS is complex and difficult to understand now. Figuring out how to tax Bitcoin would add an enormous burden to the IRS by complicating the tax code further.
Since this is really not a normal currency and not the currency that is used by the United States of America it would need to be looked at more by the congress of the United States of America. I could see however where one would argue that it should be taxed.