It's not a perfect system, but the provisions of the Anti-Defection Law tried to address what was a bigger issue in Indian politics - legislators changing sides for what turned out to be enormous sums of (undisclosed) money. In this climate, the incumbent party could bribe opposition members to prop up the government, and attempts to poach new legislators right after the elections reached ridiculous levels.
For what it's worth, while this does hinder a legislator from voting as per the will of their constituents even where they are at odds with the party line, within the Indian political system there are so many special interest parties that differ from each other in minor details of policy. In theory, the will of constituents could have been made manifest by voting for the policy adjacent party instead.
Again, it's not a perfect system, but it's attempting to fix the obvious issues that arose in India.
> In what way is this a functioning parliamentary system then?
You can ask other parliamentary systems the same questions. For example, the Australian Labor Party requires its members to pledge their support for the collective ui decisions of the caucus, which prohibits them from "crossing the floor" as well.
Just as importantly, the Anti-“Crossing the Floor” law was passed in 1985 by the Congress Party under the leadership of Rajiv Gandhi (Son of Indira Gandhi, Husband of Sonia Gandhi, and Father of Rahul Gandhi). India’s been functioning under that system for almost 40 years, and I doubt Rahul Gandhi and Congress Party will repeal that law when they come back into party. That’s because it’s their law. They wrote it.
Explicitly? No. At no point does a member sworn in as an MP have to then swear to affirm their party affiliation. In practice, however, the Anti-Defection Law deems anybody voting against the will of the party to have vacated their membership of the party, which can then be pursued to strip them of membership of the house.
Not at all. It's highly unusual for a politician to speak against the party line on a bill, if at all. The only time we ever see fracturing, if any, is around the elections, where dissatisfied members may break away or switch parties. It's not uncommon for people to switch allegiances if they were refused an election ticket as the party candidate, or for higher level politicians to form break away factions if refused the Chief Ministerial position, for example. The Anti-Defection Law allows breakaway factions only if at least 1/3rd leave en masse.
It's a feature of a multi-party parliamentary democracy - when a candidate is a representative of a party standing for any elections, and wins it, it is assumed that people voted for the candidate partly because of the electoral promises and visions of the party. Thus, if a party has made a promise to the electorate to enact some major law, and issues a whip in Parliament that all its representatives should support its passage, then they are legally bound to do so. They can still choose to abstain or even vote against it. But then the party can take action against them. (Note that this is only applicable when a party issues a whip, which democratic ones do only for laws it considers important.)
For what it's worth, while this does hinder a legislator from voting as per the will of their constituents even where they are at odds with the party line, within the Indian political system there are so many special interest parties that differ from each other in minor details of policy. In theory, the will of constituents could have been made manifest by voting for the policy adjacent party instead.
Again, it's not a perfect system, but it's attempting to fix the obvious issues that arose in India.