Question

Same-sex marriage should be legalized because it is uncivilized to deny homosexuals their civil rights. The Constitution guarantees everyone equal rights and opportunities, however, gays are denied both in terms of marriage.

is this better? I have support in other paragraphs
Ms. Sue
Yes, this is much better. :-)
Writeacher
Be sure to put a semicolon (;) after "opportunities" not a comma. Otherwise, it's a run-on.