Two points to make.
Firstly and less importantly, when a crime is committed, opportunity, means and motive are all used to proove guilt, but only motive is used after guilt has been established for the purposes of sentencing. The actual laws which state the penalties for any given crime are not absolute. It is up to the judge to decide the appropriate sentencing and as i have said many times already, any hope for equality within the judicial system is subject to pot luck that you don't end up with a racist or homophobic judge trialing the case of your attacker, victims murderer etc and allowing leniency due to bias to usurp the process of justice, and while hate crime laws do not exist within the constitution then there is no equal protection for minority groups unless you can be certain that ALL crimes motivated by simple hatred are prosecuted to the same severity as any other equal crime. All that can be done right now is ask questions as to why gay joe's murderer got sentenced to 5 years less than straight bob's if both crimes were carried out on grounds of hate. Could the judge be bias? What can we do about it? Nothing because you would then have to proove the judge is persecuting a minority group by abusing his position. Whilst there is no reason that the judge cannot be investigated for such belief it does nothing to correct the injustice already done.
Having hate crime won't necessarily stop the injustice but what it will do is make it harder to abuse the system and easier to proove another person's guilt of racism or homophobia.
Secondly, amendment 14, citizens rights, states that everybody is entitled to equal protection, it does not however say that everybody is entitled to equal rights.
Hate crime law being enforced across the nation rather than being left to local states to do the right thing (which some already have) is to the benefit of minority groups which do not yet have equal rights. How would it be worded in a 28th ammendment without upsetting a mass of the country. You cannot offer equal rights to gay people entirely because plenty of people are against gay marriage, adoption etc etc so the next best thing to further equality is to enforce a universal policy that specifically includes the gay community.
Now do you want a 28th amendment which states that it is wrong to prejudice against gay people? No you don't! Why? because that REALLY would be a step towards prosecuting on the basis of personal opinion.
Hate crime legislation protective of all, more so minorities, is likely to the biggest benefit of the gay community because it furthers equality. And if you should be homophobic you should at least see the compromise in that it does not open the door wide to the fundamental issues of marriage, adoption etc etc.
You surely must respect that you have a fantastic system in place that allows one state to be different from the next but recognise that you are nonetheless one country and obviously it has been deemed appropriate that on this issue at least, the whole nation should be enforcing the same legislation.