FPTP is increasingly undemocratic. Watch
The problem is any reform will hit the big parties. Given the choice between democratic reform and clinging onto power, they’ll always go with power.
As in, democratic, politically, in its purest form means to let the people vote for who has power in a nation, and every persons voice has equal worth.
Our current system is democratic, though not purely so, but then no nations have a pure democratic system. In ours we restrict who we give a vote to, and we don't have exactly equal worth for each vote, some peoples do end up being worth more or less due to constituency sizes, and FPTP induced safe-seats.
It is still democratic though, by global standards.
I would say a better term for the argument against it, is that its 'unrepresentative'. For example, if the conservative party put up a pig in the next election, and labour put up a chicken, and no other parties ran. The vote would still be democratic in essence, all people with a roughly equal say, would all be able to vote for the next leader.. but it would be vastly unrepresentative of what the people want as their leader (I would hope).
My arguement against FPTP isn't that its undemocratic, its that its increasingly un-representative. It was very represeanttive 50 years ago, but the nation and society has changed since, and the electoral system hasn't. As a result the gap between the people and the choices in front of them has increasingly became muddled and widdened, and given that FPTP activly prohibits new parties from forming and growing, it gives no opertunity for the poeple to actually change the system itself to something that could represent their views..
So they end up with the tyranny of "the best of the worst" type of voting, with no option to say "none of these" and absolutly no option to say "something new please"