Rayna, you seem to be seeing resentment where it doesn't exist.
It may have escaped your notice that these spaces are available to all pregnant women, not only those that are actually experiencing some mobility problems due to their pregnancy! Surely that is discriminatory? Some above mentioned their parents having MS and recovering from a brain tumour, like me these people are not necessarily entitled to a disabled badge but could often require disabled parking and other disabled privileges. I can leave the house walking fairly well but within 5 minutes barely be able to move.
I've had pregnant women look at me in disgust when I didn't get up and give them my seat on a bus. Well their 'condition' is visible, mine isn't! It seems to me that in this day and age it is incredibly judgemental to make faces at someone just because they look healthy. Being ever so slightly older now I have never drawn nasty looks at teenage boys if they don't offer their seat to me, because for all I know they could have chronic juvenile arthritis or any number of other invisible conditions.
I don't think that all pregnant women consider themselves 'entitled' but some clearly do, and they are the ones drawing the nasty glances and making assumptions about others purely on the basis of how healthy they look.
Really that parking should be there for anyone who temporarily requires some mobility assistance, for whatever reason.
As for buses, is there any real medical need for a pregnant woman to be sitting down (save for the most heavily pregnant)? Pregnancy isn't an intermittent condition, once any 'disability' aspect of it starts it will be there till you give birth, so if women have managed to walk about and get to the bus why are they any less capable of standing than anyone else? If they do feel that bad should they be out in the first place?
It just reminds me of my ex-mother-in-law who would drive into town and walk about happily shopping for hours at a time. But of course once home she couldn't possibly put the bins out because she's 'disabled'. Difference between her and me, if I can't put the bins out I wouldn't have been walking about town for hours either.
Some people manage to do all the fun things but are strangely incapable of helping out with the less fun tasks.