The salubrious benefits of PR for workers and unions was presented in this electoral reform slide show::
Speaking to unionists, I think best to speak from left perspective,
emphasizing how, under First past the post, Conservatives get more seats than they deserve time and again.
while under PR
each party gets its fair share of seats
and all (or most) votes are used to elect someone, either by name or partyÂ
(underlined might be left off as it might arouse more questions than anwers but does open door to benefits of open-list PR and STV.)
under PR, usually no one party takes majority of sets.
like-minded parties must co-operate to form working majority in the chamber.
In Canada today --
in each district, as much as 68 percent of the votes (or more) might be cast for candidates who do not win.
The waste of votes in the various districts creates dis-proportional misrepresentation overall.
Unrepresentative chambers elected by First Past The Post
example --
Mulroney's false-majority government elected in 1988Â
Mulroney won a governing majority that passed the U.S.-Canda Free Trade Agreement into law, even though a majority of the voters had voted for parties opposing free trade -- Liberals and the NDP.
I am not picking on Mulroney in particular, but 1988 is stark case where he did not take majority of votes cast but formed majority gov't and did change Canada in anti-labour way against public will.
In other elections we see somewhat similar unfairness (such as happened in NB, where a party with 61 percent of vote got all the seats),
but there a majority of people actually did vote for the McKenna government, just not in numbers implied by the 100-percent seat sweep.
Canada's recent wrong-winner elections of 2019 and 2021 are nuanced in that
in 86 percent of the country or so, Liberals did take more votes than Conservatives by something like 1M,Â
that is looking at all of the country except AB and SK.
in that 86 percent of the couintry, voters are happy to see Trudeau elected to power
A third of Conservative votes overall were cast in AB and SK, but for only 14 percent of seats,Â
and in AB and SK, Conservatives got all but one seat, far more than they deserved in AB and SK.
ALSO, even under PR, Conservatives with same vote share as 2021 would not have majority government.
(this is not a case like Malta has had where wrong-winner election meant wrong party got majority of seats. In Malta this is now impossible due to majority-government top-up if necessary
where if only two parties in house and wrong party has more seats, top-up is added to make result fair to more-pop. party.)
The way the vote was cast is easily seen by reducing the votes cast to only 100 cents - each cent represents one percentage of the votes cast. [see footnote]
Women's representation
where sometimes it is said, "if women cast 40 percent of votes, then women shoud have 40 percent of seats."
maybe better to sayÂ
if women candidates receive 40 percent of the vote, they should have 40 percent of the seats.
-goes to effective votes ideaÂ
-also does not imply that women only vote for women, which we can easily see is not (always) the case.Â
Vanuatu SNTV elections - women making up more than 40 percent of voters should take a seat in each district if women vote for women candidates. no way even in two or three or more DM district, for men to take all the seats by relative plurality (SNTV) unless women vote is split among excessive candidates, not the case in Vanuatu elections so far, few women run.
 But women are almost never elected in Vanuatu despite the opening for fairness under SNTV - because women there do not vote for women. (i don't know why...)
the ability of women candidates to get seats is equally true, even more scientifically, under PR, if women voted for women candidates.
and note that men's votes can also play a role in electing women....
so women voters do not necessarily mean women members are elected,
 but votes for women candidates would -- under PR.
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footnote:
Votes as Cents
If all the votes cast in the 2019 election were a dollar:
Conservatives would have 34 cents, ten of which would be in AB/Sask, with 24 cents spread across the rest of the country.
The Liberals would have 33 cents, two cents in AB/Sask., 31 cents spread across the rest of the country.
The NDP would have 16 cents, two in AB/Sask.
The Bloc Quebecois would have 8 cents, all within Quebec.
The Greens would have seven cents.
The People's Party would have 2 cents.
Such would be the approximate result under PR,
with each cent equalling 3.4 seats or so.
============================
Seats as Cents
If all the seats actually won in the 2019 election were a dollar
(each cent equals 3.4 seats):
Conservatives got 36 cents, 14 of which would be in AB/Sask, with 22 cents spread across the rest of the country.
The Liberals got 47 cents, no cents in AB/Sask., 47 spread across the rest of the country.
The NDP got 7 cents, less than one in AB/Sask.
The Bloc Quebecois got 9 cents, all within Quebec.
The Greens got less than one cent, spread over east and west coasts.
The People's Party got no seats so no cents.
for fuller discussion see