To answer this we have to take a look at the episode of the “Misoninim”, the complainers.

Rashi says that the term ‘Misoninim’ implies they were doing an “alila” fabricating a story to turn away from Hashem. They complained and claimed something to make Hashem angry with them, kivyachol, hoping this would cause him to turn away from them and thereby they would turn away from him.

What was this terrible complain?  

Rashi explains that they were complaining about the long and tiring journey of the past three days in the dessert.

R’ Yerucham Levovitz asks a very pointed question here. What is wrong with complaining about a long and tiring journey through the desert? All people- after traveling for some time vent some kind of frustration about how tired and exhausted they are.

I will answer this (His answer) in my own words. When I was a teenager in camp we were taken on a banana boating trip. A long yellow tube attached to a speed boat boarded by 10 guys. The idea was for the driver to try and knock us overboard and we had to hold on for as long as possible. At some point my hands turned red and then white from the tight grasp but it didn't hurt, not during or after I got off the boat. That is because I enjoyed it, it was a privilege for me to ride that boat.

The misoniinim complained, implying that they were not happy with the lifestyle they were leading; meaning, the newly acquired Torah and the fast march to Eretz Yisroel was not satisfying them, they wanted out- and they showed it by displaying their dissatisfaction.

With this we can answer the Ohr Hachaims question. Yes, they knew that they can't bring the korban Pesach and they new that you can't change the halacha but they vented their frustration their unhappiness of not being able to do the Korban pesach. Yes, no one is blaming them and they are innocent, but they are not satisfied with that, this is a fundamental difference between the two groups of people.

This stems from the way we view ourselves in keeping the Torah. Is it an ‘ohl’, ‘Yoke’ or privilege- the answer is it's both. The misonimin just saw it as an ‘ohl’ as opposed to the other group who saw it not only as a responsibility but also as a 'zchus', a privilege. That's why they are frustrated at not being able to do it even though they were not required to do it.

This is the way Hashem wants us to act. R’ Moshe Feinstein points this out by explaining that a person can perpetually exempt himself from giving terumah and masros by doing all kinds of tricks like entering from the back door or window. Despite this, Hashem did not give the kohen or Levi a portion in the land and instead commanded the rest of the nation to support them with Terumos and Maseros, even though they can be circumvented. That is because Hashem expects us to want to give them.

This shows that we are expected to act this way as the people from the pesach sheini acted. This can only work if we view the Torah not only as a responabilty but also as a privilage and a gift.

R’ Moshe adds by pointing out that this is the pshat in the bracha that we wish parents of a newborn child that they should raise her/him grow to 'Torah and maasim tovim'. Just learning Torah without implementing it is terrible, that is obvious, rather the intention of 'maasim tovim' here, is that the child should do these action which he can tehcnically avoid but he should still want to do them.