[quote=JCrusher
You have to remember Mike had no idea about Questadt. I think Mikes ego was big enough that he felt he could beat the Senate hearing which is why he didn’t take the 5th. However once he found out that Roth had a senate lawyer in his pocket Mike knew he would lose unless he took drastic measures
[/quote]
Sure, ego was part of it: Michael, the biggest gangster in America, demanding to be considered "legitimate" and actually believing it, is a massive exercise in ego. But it wasn't the only reason he didn't take the Fifth:

All Mafia higher-ups have small-time "legitimate" jobs that they use to declare some income and avoid getting nailed for tax evasion. But, when they're called before grand juries or Congress, they take the Fifth--they're not trying to convince people they're not gangsters, as Michael was obsessed with doing--they're trying to avoid being prosecuted for perjury. But Michael had two other reasons for not taking the Fifth: He fell into Roth's trap by believing that Cicci, who said he never spoke to him, was the highest ranking witness against him; and he .probably feared that if he took the Fifth, millions of his fellow Americans watching the hearing would wonder why his answers "might tend to incriminate me," and the Nevada Gaming Commission would be pressured into launching an investigation into his background and holdings.