Its a reasonable point, but I think the general feeling is that we all know they lie constantly, but that you get a chance to kick them out at the next election, or in the case of a government or party that is egregiously deceitful or incompetent there is the possibility of leaders being replaced, coalitions collapsing, votes of no confidence, essentially public and political pressure that can force a change of personnel or ultimately a new election.
So in that sense, seeing that Brexit probably has the potential to be far more destructive, irreversible and far-reaching than your average government policy you could argue that there should be more checks, balances & opportunities to change decisions than the results of general election - not less.