I think they mean, you have to "treat them with respect".  You are not rude to someone you are "treating with respect". 

While people may earn respect... sometimes people are due respect that is conferred upon them by their position.  As an adult that is one of the heads of the household.. responsibility for providing for said household.. the SP deserves respect that is due to their position in the home.

the kid does not have to respect or admire them as a person.. but they have to respect their authority in the home.

I don't think you have to respect someone to behave in a respectful manner. There are those for whom I have ZERO respect. However, I can maintain a respectful and polite manner when forced to interact with them. Some might consider that part of adulting...

Your post is a little confusing, but I think I understand what you are trying to say. 

To me, being nice is going the extra mile to do something beyond the ordinary for others. So that might be making a card for the step parent or bringing home a treat for step kids. Sometimes we choose to be nice to strangers or people who have not been nice or respectful to us, but that is a choice we make often in an effort to build a better relationship or out of a sense of altruism.

Being respectful however is a standard form of politeness that should be expected between any two people as a baseline, in my opinon. So to me being respectful is things like using please and thank you, answering questions when asked, not cussing and respecting other people's feelings and things. Basically just not being rude.

I do not think that it is useful to force anyone to be nice to someone that they do not like, and I do think that you should allow people (children and adults) to make their own minds up about who they like and who they do not like. I do think thought that respect for others should be there for everyone. We may all slip sometimes and be less than respectful on occasion when our ermotions overwhelm us (or others are disrespectful towards us) but we as adults know that we should strive to do better. 

When I was raising my children, it was called civility. It didn't mean you had to be friendly, but it meant you needed to act in a way that coincided with social mores and expected manners.  

I feel at the very least you can rise and be the better person and be civil. This does not mean I condone or support your terroristic reign over my home. But I can certainly draw my line in the sand and will not step over it. When OSS was at his worst I would walk by and say "Hello" and keep walking. If he responded, good. If he didn't I filed it away for future use. When dinner was ready I would find DH and tell him dinner is ready and walk away. It was up to him to round up his sons for dinner, not mine. I did not deliberately make food they hated but I would not make box mac and cheese and always made it from scratch. Not my problem if you hated it. I didn't add anything weird like bacon or olives or artichoke hearts or ... you get the idea.

Civility and politeness is primary. Then keep my distance as required. Lots of people are in my life and occupy the 'distance' box. They just don't know it, bless their hearts.

Yes, and it's not even "being nice" it's just teaching a kid that your treat people...good people...a certain way regardless of who they are. I've met many people I dont respect because of their actions but I'm still nice to them...

There is a difference between showing respect and being respectful IMO.
Being respectful says something about YOUR behaviour and attitude, irrespective of the person on the receiving end.
In the same way that rudeness or crass behaviour is indicative of the person displaying it.
There is very little cost to one to be respectful or decent in your dealings with others - even if you don't like them.

Appropriate behaviour is not about "being nice" or "being respectful":  to me it is about having appropriate behaviour to suit the circumstances - and this is applicable in how you raise your kids too.
You can't drill it into your kids if you yourself are ok with feral or rude behaviour.
I don't know why, but when I see shitty behaviour in kids, I can probably look no further than the parents to see some or all of the cause...

(Just my view, feel free to differ.)

You are an adult, you are the SO to SK parent. You are doing thing for SK, giving them a place to live, feeding them, buying clothes, ect.  You should be respected.   Kids have to learn that in life you must respect other people. If you like them or not.  They must respect there teachers, There friends and there bosses at work latter on. 

That the bio parent job to have there kids respect there SO. The SK must learn Disrespect has unwanted results in there,life. 

I think it comes down to feelings vs actions/behavior.

You can feel in a negative way about me but you cannot act on those feelings.

Depends what you think of when you think respect:

1.  a feeling of deep admiration for someone or something elicited by their abilities, qualities, or achievements.

Or

2. due regard for the feelings, wishes, rights, or traditions of others.

1 is earned. 2 is due.

So to me its the same thing and as the adult or elder person, society should teach us to be respectful of elder people

I agree with some of the other posts - its respect as in acting respectfully, not respect as in looking up to/admiring/having respect for someone.

I actually hate "nice" and think respectful is a better term to be honest. "Nice" behavior can be selfish or manipulative. Or it can swing too far the other way and end up in people being a doormat or not establishing boundaries for the sake of being "nice." I prefer kind over nice. To me kindness is more genuine.