If has to do with the word "marriage" coming from religion and meaning the union of a man and women. This particular union is the most efficient union in terms of social order for adults, children and the elderly. The Government, which is not supposed to establish a religion, is redefining this optimized religious term into its own form of second string religion.
There are taboos words which the Left will censor for each of its whiny groups. The term marriage is the same type of thing. The new definition is insulting for some on the Right, and they get whiny the same way to something that may not bother others. We may need to suppress this new definition to spare feelings. This is why we need free speech, so anyone can say anything, without one side having all the rules stacked in it favor; Twitter files.
For example, say A conservative government decided to lump all the members of the LBGTQ community into the new legal term, bestiality. The term bestiality currently means humans and beasts. By calling the LBGTQ community that, it would lead to purposeful confusion and will be seen by many as an insult. This is what has happened in terms of the word marriage. The anger on the Right is defensive.
When this all began, terms like civil unions were bounced around, which amounted to the same end result as marriage. This term did not try to commandeer a religious term that everyone knew would create a backslash. Everyone on both sides knew that commandeering the term marriage, would be like making a radical slur against the religious people. Why did the Left not care about the feelings of others? Because they are hypocrites. Not all the religious people will turn the other cheek and take it, like expected. Like the Twitter files are showing, we were dealing with some very shady biased characters in places of power and influence. They may need to answer for their dual standards. One standard may be the end result.
My feeling is the push toward civil unions; non religious; non socially optimized unions, is really there like abortion. It is there to help clean up the mess that was created by the social experiments of the Left. The LBGTQ free for all is a major source of disease. Civil unions by breaking up the free for all mentality, would help limit the spawning and spread of disease, just as abortion limits the number of unwanted children that would create a further deficit in terms of civil efficiency.
The term civil union may not have been strong enough to overcome the free for all mentality, that the Left had originality used to prime the pump. Marriage, due to the taboo nature to this slur definition, is like the Deficit Reduction Act, having nothing to do with the Deficit, but is more like a sugar coat for something more sinister; mop.