Try to view this whole thing objectively.
Bhagat singh wanted to kill Scott as a 'Revenge' for death of Lala Lajpath Rai, he kills Saunders by mistake.
1. Was his motive personal or for the good of the nation ? It was Personal.
2. Was the reason for killing Scott justified ? No. Scott was just doing his job assigned to him, which was Mob control. It was probably an Indian policeman who beat Lala Lajpath Rai to death.
3. Did he take action against the Indian policeman ? No.
4. Was killing Saunders a mistake ? Yes.
5. Did he confront Saunders and confirm his identity ? NO
6. Did he give Saunders a chance to defend himself ? No.
7. Once he succeed in his mission did he hand over himself to the law ? No.
Why did he not have the courage to hand himself over to the law once he killed saunders ?
Now look at his actions in bombing the Assembly with the same objectivity.
Why did he hand over himself to the police after the bombing ? but not when he killed saunders ?
Value systems have remained the same since the days of Ramayan. That is why Ramayan and Mahabharat is relevant even today.
Finally it is always Morality and Ethics that define Heroes, not people who show courage or Win battles.
How would you know it was merely out of revenge?
And how was Bhagat Singh related to Lala Lajpat Rai to seek revenge?
Lala Lajpat Rai was leading a non-violent movement, whereas Bhagat Singh's ideology was completely opposite. Had it been Mahatma Gandhi to die in that lathi charge, Bhagat Singh would still have done the same, because he believed in going for those who attacked the leaders. It is not called "revenge".
Bhagat Singh also used to write a lot. I have not read a single piece where he mentioned the word "revenge". And
were it only for revenge, a personal vendetta, why would the Congress Party support him against the hanging, even further, why would Mahatma Gandhi, while critical of his ideology, want his sentence commuted to life?
You see, Hindu principles are coded in Bhagawad Gita that was sung right before and in favor of, a great and extremely violent war.
What do you think Krishn say to Arjun when Arjun implored why should he kill his kith and kins? If your answer is anything other than, "righteousness weighs heavier than blood", then I do not know what else to say.
Why do you think the day right after Chakravyuh, Krishn took Arjun to Jayadrath? Did Krishn give Karn any chance to defend himself? Arjun waited, but Krishn, the supposed author of Gita, was unrelenting. Was that merely for Arjun's revenge from Dyut Krida? No, righteousness demands sacrifices.
So, no - it was not for revenge. Bhagat Singh's act was to show that the imposed law of the Britishers will not be tolerated to such an extent that the ideals of the age are felled one after another with complete immunity.
And I thought you knew, that it was the criticism and appeal for his surrender from senior Congress leaders that he decided to let down his guard.