This probably isn’t as constructive as it could be, but arguing that something is or isn’t a concern based on multiple definitions of a word is generally ineffective when the root cause of the argument is over the multiple definitions of the word.
“Without wanting to have the same arguments again (not the point of this thread), there are two overlapping uses of the verb ‘discriminate’.”
“I support the legal definition of marriage which is the voluntary union for life of one man and one woman to the exclusion of all others. I oppose any attempt to redefine it.”
Considering the source for the modern “legal” definition of marriage in most of the “Western World”, I think that is far to narrow an attempt to define it. For the judeo-christian perspective, please consult this handy chart: