Essentially, the two sentences express the same thing: people who do not have their belongings anymore will turn into miserable people. For most people they will be interchangeable. There is a slight difference in the emphasis.
Using the present perfect emphasizes on the result. It talks about people who have had their things taken before now, at any point in the past; it doesn't matter when exactly, what matters is that they do not have them now. The result is important.
Using the past simple simply talks about an action at a moment in the past. In this case I would think we are talking about one particular occasion when someone took their belongings because I do not see anything in the sentence that implies repetition.
Whether to use "have had" or "had" depends on the context. If you are talking about a time when many things happened, one of which was that people had their belongings taken, then I would use the past simple because there is one particular past moment we have in mind. If there isn't one, and we want to say: "people who do not have their belongings now", then I would choose the present perfect.
About the second pair, you are right in your assumptions. Let me expand the phrases. The first one is: "people who normally/usually smoke". the second one is: "people who have ever smoked before/in the past (whether regularly or even once)".
When talking about things in the past, the past perfect happens before the simple past.
In your example
If someone feels that they had never made a mistake in their life, then it means they had never tried a new thing in their life.
had never made and had never tried are two actions which were started and ended in the past compared with how the person feels (present). The equivalent would be
If someone feels that they never made a mistake in their life, then it means they had never tried a new thing in their life.
where never made is nearer in time than had never tried since one would have had to try before failing.
I had called you
I had gone to the wash room
could individually use the simple past
I called you
I went to the wash room
with similar meaning, however, using past perfect sets up a scenario for something in the more recent past
I had called you before I went to the wash room
I had gone to the wash room before I called you
To answer where you were when they called:
I had gone to the wash room when you called me
means you were in the wash room (past perfect) when the person called
I went to the wash room when you called me
means you heard the phone ring then went (simple past) to the wash room
Best Answer
To begin with, look at your sentence:
I recommend looking at it in two parts:
Sentence 1 tells you that members of the 16th Lok Sabha worked harder in the budget session. The "budget session" refers to the present budget session, that happened just now, or during the 16th Lok Sabha, if you will.
Sentence 2 introduces a comparison- with how much they have worked in the last 10 years. Now, the idea behind using "have" is to introduce a continuum, a matter of fact that "has been happening" regularly over the past 10 years.
If you use "had" instead, it gives the idea that something HAS happened at a certain point in time, and then that's it. It didn't happen anymore. For instance:
Notice how "had" is used to indicate what they did just once, that is last year.
Again, if you now use "have" in the same sentence, see how you get a different meaning:
Here, "have" tells you about something that hasn't occurred just once, but has been occurring regularly over a course of time, that is five years.
It's interesting to note that using "had" in part 2 of your original sentence wouldn't make it incorrect, technically. There is a very fine line between using "have" and "had" to denote a continous action in the past tense. As I explained with my previous example, if you use "had" in sentence 2, it indicates that the members of the Lok Sabha had worked up until now, which doesn't fit in well with sentence 1.
And lastly, do take a look at this question on the EL&U site: How do the tenses and aspects in English correspond temporally to one another?. It should give you a clear picture about everything.