The most obvious argument against denying people care on the grounds of unhealthy lifestyle is: where do you stop? If you deny care to smokers, drinkers or fat people, why not people who indulge in other self-harming activities that may require medical attention? Aside from climbing and skiing accidents, most serious sportspeople seem to have permanently damaged something that gives them trouble in later life. People don't have to indulge in the activity that spreads chlamydia. What advertisers call today's hectic lifestyle leads to what doctors call stress-related illnesses. GPs and consultants have the right to advise and encourage people not to play contact sports, go potholing, sleep with strangers, work 60-hour weeks or fail to wrap up warmly, but no one would argue they shouldn't treat people who fail to follow that advice, particularly when they present with unrelated illnesses.
Of course, smokers do the Treasury a huge favour by paying monster consumption taxes on their habit and then forfeiting their pension by dying young. Why shouldn't rugby players need health insurance to cover their sports activities, as skiers already do?
If people pay the full external costs (e.g. insurance for increased risk of ill health) of their lifestyle choices, there is no moral reason for retrospectively punishing smokers, drinkers or sports players by denying them healthcare.