My moral standards are based on empathy
Empathy is the human ability to share in feelings and emotions, by using our empathy we can know which of our actions hurt our fellow human, which help them and which ones don't affect them negatively or positively.
Adultry hurts our fellow human
Rape hurts our fellow human
Stealing,
Killing,
Attacking (causing physical harm)
Causing emotional harm
Disrespect hurts fellow humans
Mistreating yourself is also immoral, because the list applies to everyone human even if the victim and perpetrator are one and the same.
The list goes on. But there's more to my morality than just not hurting others.
Consent is very important to humans, and even though in many cases animals don't take harm from sexual actions with humans they still can't consent so having sex with them is essentially rape.
Even lies that never affect anyone are immoral, because to lie you are manipulating and one lie leads to the next, and be a lie can not make anything that is good.
I could go on forever telling you how you don't need an old book to be moral but I won't, because it's honestly dumb to think that everyone who doesn't follow your God struggles with lack of moral compass, the human feeling of empathy is much better better equipped as a moral compass than your book.
And yes, I don't consider homosexuality immoral because in terms of empathy based morality it's perfectly harmless.
This is just subjective morality. The issue here is it's impossible to follow. What is immoral to you may not be immoral to another. So who is right?
You may consider this an extreme example, but it's still completely valid. And with it being estimated that 1 in 25 Americans are sociopaths, it's actually not that extreme. But if a sociopath finds their behavior of demeaning others, or violence against others, as acceptable, going by their personal moral compass, who can argue with them?
At the end of the day you are still setting a list of rules of right and wrong.
If it's an issue of 'hurting' others, then what may hurt one may not hurt another.
You take a happily married couple, and one of them cheats, it would hurt their partner. If you have two miserably married people and one cheats the other may not even care. So is cheating right or wrong? Is the cheating ok with one, but not with the other?
Now morality comes down to each individual.
What about a girl who grows up abused by her father? Many times these girls grow into women who accept abuse because they feel that's all their worth. Or in some cases they feel it's what they deserve. Does an abusive person do wrong by abusing that girl?
That's the issue with subjective morality. It is a constantly moving and flowing sea with no real borders or boundaries. And over time it allows the acceptance of previously unaccepted behaviors that were once deemed harmful. Homosexuality is a valid example. It was once deemed an unhealthy and harmful practice. Now it is taught to young children. Due to that we now have 'gender fluid' issues. Now we are being taught to learn new terms to accept people of varying degrees of sexuality. What will be the next previously unhealthy morality issue to be pushed an accepted?
You can have moral ideas without the bible or God, but what value does that moral belief have if it constantly changes itself to accept what was once considered immoral? Are you truly standing on morality at that point? How far are you willing to accept previously immoral acts before you, subjectively, decide it's crossing a line?
And when that line is reached, might your 'rigid' morality not be hurtful to those seeking acceptance? Which then causes you to break your own morality.
If a man decides he should have the right to have consensual sex with a 13 year old and you 'morally' deny him that right, is that not 'hurting' that man by denying him his rights due to your morality?
You think of biblical morality as such a bad thing, but at least that morality is clearly defined and stands in one spot. Your subjective morality will eventually fail because you can never tell someone something is wrong at the risk of 'hurting' them.