That's like saying "should we allow people against abortion get pregnant/have children?"
If you are like me and for gay marriage then you are doing it because you support people's freedom. To then turn around and say people who don't agree with me shouldn't be allowed to marry is ridiculously hypocritical. It serves no purpose other than spite and goes against all of the values anyone who believes in the freedoms that we have been campaigning to encompass to the LGBT community.
This is a yes to the above but a no to marriage being recognized by the state. No one should be denied their rights because of there opinions. With the ONLY possible arguable exception (not saying I'm for or against such an exception only that I feel all others should be rejected automatically on principal with no debate or reasoning necessary) being a small one of the right to privacy, and only in so far and limited to ascertaining probable cause that that opinion is causing you to break the law or interfere with the rights of others (being against gay marriage and in charge or such applications invites inspection if you may be denying people because they are gay, being against all taxes means that the IRS could take a second glance at your tax return). On the other hand marriage is a religious institution, and as such it should have no relation to the government because of the separation of church and state in our first amendment. That does not mean however that the government can or should not have a separate institution that mirrors the concept or purpose. I feel that all government marriages should instead be civil unions, the requirements of which are to be addressed without any religious bias or context. On the other hand the government will not be allowed in any way shape or form to influence whether any religious institution does or does not recognize any different types of marriage. This is in keeping with the separation of church and state in the constitution.
It is absolutely oppressive to not allow people to marry just because of their views.
Being against gay marriage is a belief and/or an opinion, and people are entitled to their own beliefs/opinions: see our Constitution's First Amendment. So yes, people who are against gay marriage should be able to marry.
Just call it something different. I'm not completely against it, but marriage is a religious ceremony. I'm not saying you can't to live together or adopt, or have to call it a "Civil Union." But don't call it marriage.