Talk about a slow news day. Pointing out that attitudes about lgbt's in the US is "diverse" can barely constitute as a warning. At worst it can be called a "friendly reminder." Here's what a warning looks like, on the UK's page on Saudi Arabia:
"Homosexual acts and adultery are illegal and can be subject to severe sanctions. "
https://www.gov.uk/foreign-travel-advice/saudi-arabia/local-laws-and-customs
Or Nigeria...
"Homosexuality is generally viewed as unacceptable in Nigeria. The ‘Same Sex Marriage Prohibition Bill’ allows lengthy prison sentences for those entering into a same sex marriage, those witnessing, aiding or abetting a same sex marriage, the operation and support to gay clubs, societies and organisations and the public display of same sex relationships."
Or Uganda...
"Homosexual activity is illegal and not tolerated in Uganda’s conservative society. Public displays of homosexuality like kissing in public places could lead to arrest and imprisonment. An Anti-Homosexuality Act was signed into law in early 2014 which increased penalties and created new criminal offences. However it was overturned a few months later."
I'd say the UK's travel advisory regarding the US, when looked at in perspective, is perfectly reasonable.