Is, "We need to have a National discussion about X", the latest doubletalk for My way or the highway, or do we really need to discuss?

Civil discourse is an endangered species. The loudest and most extreme views get rewarded with publicity, hence it has become a self-licking ice cream cone.
Regarding some of the issues you have raised, SGM (Join to see) -
1. Immigration. Think of it like you have a problem with ants getting in the house. ( I mean no insult, just drawing a metaphor) You can step on the ones you see, put out traps, or try to seal the house... but what really works is finding out what attracts them in the first place and eliminating that. Yes, we need border enforcement, but what we really need to do is eliminate the "free stuff" that draws them in and keeps them here. Next, enforcement needs to be directed at employers who knowingly hire illegal workers in order to profit from the cheep labor. Onerous fines indexed for number of employees and applied equally to the company and the hiring official would discourage the practice nicely. What remains would be far simpler to deal with then the scope of the problem today.
2. Gun control. Funny thing about current initiatives, executive and legislative, is that not only do they make it harder for law-abiding citizens to procure and exercise their legally purchased weapons, it is encouraging hoarding of ammunition and purchases of guns is through the roof on fears of limitations in the future. Ultimately, these efforts if successful will make it harder for you and me, and not encumber criminals, terrorists, or those bent on mayhem at all. The ineffectiveness of the measures proposed lead me to conclude the effort is facetious and not really trying to affect the problem at all, but rather create an "issue" for the upcoming election.
3, Welfare. Interesting how "necessity" has been redefined in recent years. Now, cell phones are a "necessity". As is internet access, television, junk food with EBT cards, and the like. Why, you might ask? Simple. To keep the masses (read voters) dumb, fat, happy, and dependent. A safety net is just that. It is not a way of life. Not long ago a similar mistake was made extending unemployment payments for years. Pretty soon, people stopped working or even looking for work. If that is your desired end state, you are not worthy of elected office.

Let me throw in an issue of my own, protesting as a cottage industry. People are being paid to be upset, loudly shouting, waiving professionally made signs, and generally behaving in a disgusting manner. This intentionally disrupts and subverts civil discourse, and those behind it should be exposed for the frauds and riot-inciting buffoons they are. I'll bet that the answers to who is behind this Astroturf version of "grassroots movements" would be very illuminating.

It's both. When you considering the consider that this statement is uttered only during election campaigns and after some sort of crisis/tragedy/disaster, it is always agenda driven. Worse than that, whenever that statement is uttered, the intended meaning is "how can we, the government, get involved and otherwise get better control of the people?" The only truth in the statement is that sometimes there does need to be a discussion, but the type of discussion necessary will never seem to take place. Why? Everyone and everything is too politically, ideologically, and emotionally charged. That is to say, every discussion after the phrase "thanks for coming" devolves into finger pointing, blame game, scapegoating, and generalized accusations. In other words, nothing can be achieved because all logic and intelligence has gone right out the window at the outset.

I have made the suggestion several times. You should try to honestly argue the other view. That will provide more insight that you may imagine. After you have done then join a discussion with an open mind.

Most of the problem is an opinion and a closed mind when hearing anything other than that opinion.