> Is being philosophically critical of something automatically hostile?
Not in terms of the Equality Act. You can be as critical as you like in private, or outside the workplace as I understand things.
But if you voice those criticisms directly to someone in the protected class in the workplace, then you’ve crossed the line.
So, eg, telling a gay person to their face that you oppose gay marriage & all gay people are going to hell might be your strongly held philosophical (or religious in this case) belief, but the act of voicing it to the individual in the protected class breaks your employers obligations under the Equality Act in the UK & they would be entitled to fire you for it. The same goes for persistently mis-gendering a trans person (quite apart from it being extremely rude of course!) as gender re-assignment forms a protected class in law.
(Obviously, this is as I understand things & not the opinion of a legal expert in these matters.)