I agree with the spirit of what you're saying, but...
While we are free in Christ, not everything is beneficial and not everything edifies (see 1 Corinthians 10:23).
The yoga discussion could be linked to the eating meat sacrificed to idols passages (See 1 Corinthians chapters 8 & 10). If one in good conscience can eat it, it might be permissible but they are not thinking of their brother and so should limit their freedom before causing a weaker brother to sin, thereby making themselves guilty as well. However, it says not to have the one who abstains nor the one who eats judge the other because God is the judge. If you disagree, you have a right to your own opinion. People that think it’s not a good practice are here to warn those that don’t know and would listen. In the end, whatever each person does, let them do it as for the Lord and not man.
I don’t think God would find it honoring to Him to be using the same practices when the Bible speaks so much against idolatry and not to bow down to idols nor to worship like the pagan nations, but that’s where people will distinguish between “worship” and “exercise.” Yet if it’s “just an exercise” then why can’t believers go and physically bow down in front of a statue? Why would God get mad if we could argue we’re “just stretching” our body in that position? What message would it send if we were to go and “stretch” in that way bowing our body in front of the statue of some other religion? Why would you have to stretch in that specific way at that specific location? You can stretch in any other way and anywhere else.
You’re right that the LGBT movement has wrongly appropriated God’s beautiful rainbow. I would agree that it does not mean we have lost the true meaning of it, God’s promise not to flood the world again after Noah. It’s a symbol of hope. I also enjoy pictures or art that includes rainbows as well as using the colors of the rainbow. Nothing wrong there. However, with the meat sacrificed to idols again, considering a fellow brother who may be newer in the faith or not as strong in our beliefs, to give the wrong message to them? There are Christians that support the LGBT movement and have rainbow flags hung up on their churches. I know what the Bible says though and I can’t have that on my conscience. We are to love people, but not their sins (and this is just one of many).
If you want to fly a rainbow flag on your porch and “take back” the rainbow, go for it but I wouldn’t want to convey the wrong message. It’d have to have something to distinguish it and even then it’d probably end up being like something you’d see on a bumper sticker and I don’t think it sounds particularly loving. To any outsider that is gay it would seem to be yet another rejection from Christians. They are welcome, but that doesn’t mean we support the lifestyle. Like we non-smokers would not encourage a smoker to go outside and finish their pack of cigarettes that is slowly killing them. Any sin is like that “for the wages of sin is death” (Romans 6:23).
I think people can use their own routines to stretch their bodies, but when you use the specific poses involved in yoga that the Hindus and occultists like Aleister Crowley use to worship other gods, you’re walking some perilous ground. Crowley promoted yoga and wrote “Eight Lectures on Yoga,” “The Magical Record of the Beast 666,” as well as other occult books. Google it and look at the symbolism and titles of his books that include the all-seeing-eye pyramid, eye of Horus, pentagrams….
One could argue well they appropriated the number 6, pyramids, eyes, the way they draw the stars etcetera. However, does that mean we as Christians have to skip the number 6 when we count? That we cannot use pyramids in math class? That we can never draw our stars like they draw pentagrams? That we can never use a single dollar bill because of the eye pyramid symbols on it? That we can’t cover one eye when we go to the eye doctor for an eye exam or do one for our driver’s license? No! But are we going to wear the occult symbols on our t-shirts and bumper stickers for the world to see and get the wrong idea that we support those things? I’ve seen people’s license plates randomly include three sixes and it seems random, but also ones on purpose that have like “BST666” or something like it in yellow and black that makes it clear they are putting it up either in support of the “beast” that is Satan or the ideas behind Satanism (e.g. “do as thou wilt”) even if they don’t believe in a literal Satan (there are 2 types of Satanists).
Why do you think yoga’s so popular today? Satan is the ruler of this world. If you read the Bible, the book of Revelation talks about a great falling away and many worshiping the antichrist. They’ll believe lying signs and wonders. They want one world religion worshiping the antichrist and for people to “unite” under this system.
If you still feel okay doing it then yes you can use your freedom in Christ to do it, but should you? What if your brother goes “further” down the path into occult, New Age, Hindu, or other beliefs and either synchronizes the beliefs or completely leaves the faith? Look up kundalini yoga and how they visualize serpents crawling up your spine and awakening your “third eye.” Some of those people literally get possessed. I wouldn’t want that on my conscience.
Again, not here to judge or criticize, but to warn and hopefully some people heed the warnings. It’s done out of love. If you want to continue practicing yoga, then all we can do is agree to disagree and pray for you and any other unwitting participants.