I don't see the relevance in your being "from the UK," but it was also common for me to shower (naked, of course, as if that was not implied) with other guys from a gym class or various athletic teams in school. At no time did I get sexually aroused, as you say you did, and at no time did I observe other guys getting sexually aroused. It is fair for you to suggest some men should cover up if they are uncomfortable with being naked or having other men perving on them, but that suggestion misses the point repeated in this, and similar, threads. The point is that such men are vilified for their acts of modesty, and that vilification exposes a particular kink -- perhaps one you enjoy -- that some men have for seeing other men naked.