Tuilagi received the suspension, which rules him out of Tigers' Aviva Premiership final clash with Saracens and next month's Churchill Cup, after his brutal three-punch assault on Northampton winger Chris Ashton.
The 20-year-old, a contender for a place in Martin Johnson's World Cup squad, landed two powerful left-handed punches on the England flyer, before completing the combination with a crunching right hook which left Ashton needing stitches to a cut near his left eye.
Both players were sin-binned over the incident, but Tuilagi was subsequently cited.
The RFU's disciplinary hearing, chaired by Blackett, had dealt with the offence as a top-level entry point, but an initial 10-week ban was reduced by 50% due to mitigating factors - including Ashton's push on Tuilagi, the Leicester man's inexperience and his guilty plea.
The perceived leniency of the punishment has been criticised in sections of the media but when asked if he had any regrets over the length of the ban, Blackett told BBC Five Live: "No, not at all. The ban is appropriate for the type of offence.
"Everyone has a view but all you can do as someone sitting in judgement is listen to the evidence before you apply the regulations or the law and do your best.
"Sometimes we get it right, sometimes we get it wrong. I am comfortable with this decision. It may be lenient but it is in the right ball park.
"According to the IRB regulations and our own regulations one must take into account the age and experience or the youth and inexperience of a player, because somebody who is younger is not likely to be as mature in his approach to the game.
"He is likely to react differently and it is taken in all types of sentencing that a young and immature person is going to have a lesser sentence than someone who is older and should know better."
Blackett also disagreed when it was put to him that Tuilagi's third punch was "as bad as it gets".
"It wasn't," he said. "Because it did not break a bone, it did not cause concussion and it did not knock somebody over. It looked very bad in slow motion, I accept that because the head was knocked back, but in full time perhaps it was not quite as bad as it looked."
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