Perhaps, but do you really want to bet your freedom on the whims of some IRS agent? The penalty for underreporting income is steep, especially when you're talking about tens of thousands of dollars (as many Steemsters are). And there's no statute of limitations for underreporting income.
Furthermore, unlike sales of Facebook or Reddit accounts, the Steem blockchain is a public record and lasts forever. It's as easy for the IRS to to read the chain and see who made what and when as it is for you or me to do so.
The IRS is already cracking down on unreported crypto income. Witness its sweeping subpoena issued to Coinbase.com. Cracking down on Steem would be so much easier for them--no subpoena required.
I admire your desire to be legal, lawful and moral all at the same time :)
I myself have concerns about the well being of the witnesses to steem.
You know I'm not starting like that without a "However"....
On your point about "blockchain is a public record and lasts forever" for records of earnings:
Have you ever used the "Convert to Steem" tool?
Have you noticed it does no make a record of when the transaction was started or How many SDBs were used to buy the steem? ... Did you also know that the conversion is a process subject to the decisions of the witnesses? If all the witnesses agreed one day, they could set the value of SDB to one cent.