There is something oddly twisted in this argument. Every individual has a right to “impose” their beliefs on others. The gay lobby is working very hard to impose its beliefs on others. The reason, I would hope, that individuals are Catholic is because their beliefs are in accord with Church teaching. That means the beliefs of those individuals reflect and are reflected by Church teaching. Every Catholic has a right, as an individual, to “impose” their beliefs on the state merely as a matter of having the political right to do so within a democracy.
If Catholic beliefs are true beliefs regarding the nature of human beings and what it is that makes a just society, then by following your notions, you would be advising that the most completely true principles about ethics and politics are those which will have no place in this democracy you seek to build premised on the separation of Church and state. By default, you will end up with every inferior political and moral notion being allowed but the best principles being disallowed merely because they happen to be those endorsed by the Church or churches in general.
The logic that ought to be invoked is to allow sound moral and ethical thinking, not matter where it is sourced, to determine democratic governance and judicial policy. Frankly, I don’t care if a Methodist attempts to impose their “beliefs” on me provided those beliefs have been shown to reflect sound judgements. That is the reason, by the way, that I subscribe to Church teaching, it has been tried and found true for 2000 years and before that in Judaism.