Political parties are equally capable of stifling debate as they are promoting it. There was a lovely moment on R5 a couple of years ago when they were doing their MP's panel. The MP's from all three parties had to leave to attend a vote. In all innocence Gaby Logan asked them what they were voting on. None of them knew. Basically all they do is walk through a division according to the the direction of the whip
The health of a democratic model lies in the choice and freedom to make those choices, if you choose to express that through a constituted party or series of parties then they're just models.
I'm not so sure that parties don't ultimately become a corrupting influence myself. Remember our system is supposed to be based on the election of a representative to represent the people who live in an area of the country.
What happened is that MP's started forming voting pacts with each other rather than voting in accordance with their electorates wishes. From these cosy arrangements emerged parties. Ultimately the MP starts to serve the party first and the voter second. If parties were done away with, and MP's could debate unencumbered by the threat of party whips we might get better decisions and much more involvement and participation from a bottom up model. A party line is as likely to restrict debate as it is to promote it
Ultimately what happens in one party states is that you get factions within the party, and these do start to become parties within a party. It's not as far removed as you might think from the parliamentary process. You still elect your representatives but do so based on your assessment of their ability rather than your assessment of the party they represent, and by proxy therefore, someone elses ability
In a strange way, I was happy to vote for the SNP based on their policy programme, but am denied the opportunity to do so (democracy?). The nearest I could get to voting SNP was Labour who I felt might join a popular front with them. In this imperfect system I end up endorsing a party I don't want to endorse in the hope of making a speculative long distance connection with another party.
Personally I still think there is something to be said for having the option of a negative vote, that is to say voting to remove a vote from the tally of a nominated party. It's still representative and would be closer to my strength of feeling in my case. I'd happily have voted one off the Tories, and at least that way won't have been conned into voting Labour, and especially since Labour will doubtless interpret my vote as an endorsement, when it isn't